1001ict programming 1 semester 1, 2011 lecture 8 course review 1

1001ICT Programming 11001ICT Programming 1Semester 1, 2011Semester 1, 2011

Lecture 8Lecture 8

Course ReviewCourse Review

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Java Review TopicsJava Review TopicsPrimitive Data TypesExtended Data TypesVariablesArithmetic ExpressionsBoolean ExpressionsAssignmentData Conversion Input / OutputFlow of ControlArrays (revisited)MethodsClass Libraries

Java Primitive Data TypesJava Primitive Data Types

There are eight primitive data types in Java

Four of them represent integers◦byte, short, int, long

Two of them represent floating point numbers◦float, double

One of them represents characters◦char

And one of them represents boolean values◦boolean

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Java Primitive Data Types - NumericJava Primitive Data Types - Numeric

The difference between the various numeric primitive types is their size, and therefore the values they can store:Type

byteshortintlong

floatdouble

Storage

8 bits16 bits32 bits64 bits

32 bits64 bits

Min Value

-128-32,768-2,147,483,648< -9 x 1018

+/- 3.4 x 1038 with 7 significant digits+/- 1.7 x 10308 with 15 significant digits

Max Value

12732,7672,147,483,647> 9 x 1018

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Java Primitive Data Types - Java Primitive Data Types - charchar

A char variable stores a single characterCharacter literals are delimited by

single quotes:'a' 'X' '7' '$' ',' '\n'

Example declarationschar topGrade = 'A';

char terminator = ';',

separator = ' ';Note the distinction between a

primitive character variable, which holds only one character, and a String object, which can hold multiple characters

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Java Primitive Data Types - Java Primitive Data Types - booleanboolean

A boolean value represents a true or false condition

The reserved words true and false are the only valid values for a boolean type

boolean done = false;

A boolean variable can also be used to represent any two states, such as a light bulb being on or off

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Java Extended Data Types - Java Extended Data Types - StringString

A string of characters can be represented as a string literal by putting double quotes around the text

Examples

"This is a string literal.""123 Main Street""X"

Every character string is an object in Java, defined by the String class

Every string literal represents a String object

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The string concatenation operator (+) is used to append one string to the end of another

"Peanut butter " + "and jelly"

It can also be used to append a number to a string

A string literal cannot be broken across two lines in a program

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Java Extended Data Types - Java Extended Data Types - StringStringThe + operator is also used for arithmetic

addition

The function that it performs depends on the type of the information on which it operates

If both operands are strings, or if one is a string and one is a number, it performs string concatenation

If both operands are numeric, it adds them

The + operator is evaluated left to right, but parentheses can be used to force the order

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Because strings are so common, we don't have to use the new operator to create a String object

title = "Java Software Solutions";

This is special syntax that works only for strings

Each string literal (enclosed in double quotes) represents a String object

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It is occasionally helpful to refer to a particular character within a string

This can be done by specifying the character's numeric index

The indexes begin at zero in each string

In the string "Hello", the character 'H' is at index 0 and the 'o' is at index 4

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Once a String object has been created, neither its value nor its length can be changed

Thus we say that an object of the String class is immutable

However, several methods of the String class return new String objects that are modified versions of the original

Java Extended Data Types - Java Extended Data Types - StringStringSome Java String methods

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Method Use

char charAt(int index) s.charAt(3);

boolean equals (String str) s.equals(“abcd”);

int length() s.length();

String trim() s.trim();

String substring(int offset, int endIndex) s.substring(2,10);

String replace(char oldChar, char newChar) s.replace(‘a’, ‘x’);

String toLowerCase() s.toLowerCase();


What if we wanted to print a the quote character?

The following line would confuse the compiler because it would interpret the second quote as the end of the string

System.out.println ("I said "Hello" to you.");

An escape sequence is a series of characters that represents a special character

An escape sequence begins with a backslash character (\)System.out.println ("I said \"Hello\" to you.");

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Some Java escape sequencesEscape Sequence

\b\t\n\r\"\'\\

Meaning

backspacetabnewlinecarriage returndouble quotesingle quotebackslash

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Java Extended Data Types - ArraysJava Extended Data Types - Arrays

An array is an ordered list of values

0 1 2 3 4 5 6 7 8 9

79 87 94 82 67 98 87 81 74 91

An array of size N is indexed from zero to N-1

scores

The entire array

has a single nameEach value has a numeric index

This array holds 10 values that are indexed from 0 to 9

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Java VariablesJava Variables

A variable is a name for a location in memory

A variable must be declared by specifying the variable's name and the type of information that it will hold

int total;

int count, temp, result;

Multiple variables can be created in one declaration

data type variable name

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Java VariablesJava Variables

A variable can be given an initial value in the declaration

• When a variable is referenced in a program, its current value is used

int sum = 0;int base = 32, max = 149;

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Java Variables - Java Variables - finalfinal

A constant is an identifier that is similar to a variable except that it holds the same value during its entire existence

As the name implies, it is constant, not variable

The compiler will issue an error if you try to change the value of a constant

In Java, we use the final modifier to declare a constant

final int MIN_HEIGHT = 69;

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Java Variables - Java Variables - finalfinal

Constants are useful for three important reasons◦First, they give meaning to otherwise

unclear literal values For example, MAX_LOAD means more than the

literal 250

◦Second, they facilitate program maintenance If a constant is used in multiple places, its

value need only be updated in one place

◦Third, they formally establish that a value should not change, avoiding inadvertent errors by other programmers

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Java Arithmetic ExpressionsJava Arithmetic Expressions

An expression is a combination of one or more operators and operands

Arithmetic expressions compute numeric results and make use of the arithmetic operators

• If either or both operands used by an arithmetic operator are floating point, then the result is a floating point

AdditionSubtractionMultiplicationDivisionRemainder

+-*/%

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Java Arithmetic Expressions - Java Arithmetic Expressions - // and and %%

If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded)

• The remainder operator (%) returns the remainder after dividing the second operand into the first

14 / 3 equals

8 / 12 equals

4

0

14 % 3 equals

8 % 12 equals

2

8

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Java Arithmetic Expressions - Operator Java Arithmetic Expressions - Operator PrecedencePrecedence

Operators can be combined into complex expressionsresult = total + count / max - offset;

Operators have a well-defined precedence which determines the order in which they are evaluated

Multiplication, division, and remainder are evaluated prior to addition, subtraction, and string concatenation

Arithmetic operators with the same precedence are evaluated from left to right, but parentheses can be used to force the evaluation order

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Java Arithmetic Expressions - Operator Java Arithmetic Expressions - Operator PrecedencePrecedence

What is the order of evaluation in the following expressions?a + b + c + d + e

1 432a + b * c - d / e

3 241

a / (b + c) - d % e2 341

a / (b * (c + (d - e)))4 123

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Java Boolean ExpressionsJava Boolean Expressions

A condition often uses one of Java's equality operators or relational operators, which all return boolean results

== equal to!= not equal to< less than> greater than<= less than or equal to>= greater than or equal to

Note the difference between the equality operator (==) and the assignment operator (=)

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Boolean expressions can also use the following logical operators

! Logical NOT&& Logical AND|| Logical OR

They all take boolean operands and produce boolean results

Logical NOT is a unary operator (it operates on one operand)

Logical AND and logical OR are binary operators (each operates on two operands)

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The logical NOT operation is also called logical negation or logical complement

If some boolean condition a is true, then !a is false; if a is false, then !a is true

Logical expressions can be shown using a truth table

a !a

true false

false true

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The logical AND expression

a && b

is true if both a and b are true, and false otherwise

The logical OR expression

a || b

is true if a or b or both are true, and false otherwise

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Expressions that use logical operators can form complex conditions

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if (total < MAX+5 && !found)

System.out.println ("Processing…");• All logical operators have lower

precedence than the relational operators

• Logical NOT has higher precedence than logical AND and logical OR


A truth table shows all possible true-false combinations of the terms

Since && and || each have two operands, there are four possible combinations of conditions a and b

a b a && b a || b

true true true true

true false false true

false true false true

false false false false

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Specific expressions can be evaluated using truth tables

total < MAX found !found total < MAX && !found

false false true false

false true false false

true false true true

true true false false

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The processing of logical AND and logical OR is short-circuited

If the left operand is sufficient to determine the result, the right operand is not evaluated

•This type of processing must be used carefully

if (count != 0 && total/count > MAX)

System.out.println ("Testing…");

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Java AssignmentJava Assignment

An assignment statement changes the value of a variable

The assignment operator is the = sign

total = 55;

• The expression on the right is evaluated and the result is stored in the variable on the left

• The value that was in total is overwritten

• You can only assign a value to a variable that is consistent with the variable's declared type

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The assignment operator has a lower precedence than the arithmetic operators

First the expression on the right handside of the = operator is evaluated

Then the result is stored in thevariable on the left hand side

answer = sum / 4 + MAX * lowest;

14 3 2

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The right and left hand sides of an assignment statement can contain the same variable

First, one is added to theoriginal value of count

Then the result is stored back into count(overwriting the original value)

count = count + 1;

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Java Assignment - OperatorsJava Assignment - Operators

Often we perform an operation on a variable, and then store the result back into that variable

Java provides assignment operators to simplify that process

For example, the statementnum += count;

is equivalent tonum = num + count;

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There are many assignment operators in Java, including the following

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Operator

+=-=*=/=%=

Example

x += yx -= yx *= yx /= yx %= y

Equivalent To

x = x + yx = x - yx = x * yx = x / yx = x % y


The right hand side of an assignment operator can be a complex expression

The entire right-hand expression is evaluated first, then the result is combined with the original variable

Thereforeresult /= (total-MIN) % num;

is equivalent toresult = result / ((total-MIN) % num);

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The behavior of some assignment operators depends on the types of the operands

If the operands to the += operator are strings, the assignment operator performs string concatenation

The behavior of an assignment operator (+=) is always consistent with the behavior of the corresponding operator (+)

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Java Assignment - Increment and Java Assignment - Increment and DecrementDecrement

The increment and decrement operators use only one operand

The increment operator (++) adds one to its operand

The decrement operator (--) subtracts one from its operand

The statementcount++;

is functionally equivalent tocount = count + 1;

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Java Assignment - Increment and Java Assignment - Increment and DecrementDecrement

The increment and decrement operators can be applied in postfix form

count++

or prefix form

++count

When used as part of a larger expression, the two forms can have different effects

Because of their subtleties, the increment and decrement operators should be used with care

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Java Data ConversionJava Data Conversion

Sometimes it is convenient to convert data from one type to another

For example, in a particular situation we may want to treat an integer as a floating point value

These conversions do not change the type of a variable or the value that's stored in it – they only convert a value as part of a computation

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Conversions must be handled carefully to avoid losing information

Widening conversions are safest because they tend to go from a small data type to a larger one (such as a short to an int)

Narrowing conversions can lose information because they tend to go from a large data type to a smaller one.

In Java, data conversions can occur in three ways◦assignment conversion◦promotion◦casting

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Assignment conversion occurs when a value of one type is assigned to a variable of another

If money is a float variable and dollars is an int variable, the following assignment converts the value in dollars to a float

money = dollars

Only widening conversions can happen via assignment

Note that the value or type of dollars did not change

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Promotion happens automatically when operators in expressions convert their operands

For example, if sum is a float and count is an int, the value of count is converted to a floating point value to perform the following calculation

result = sum / count;

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Java Data ConversionJava Data ConversionCasting is the most powerful, and

dangerous, technique for conversion

Both widening and narrowing conversions can be accomplished by explicitly casting a value

To cast, the type is put in parentheses in front of the value being converted

For example, if total and count are integers, but we want a floating point result when dividing them, we can cast total

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Java Input / OutputJava Input / Output

The Scanner class provides convenient methods for reading input values of various types

A Scanner object can be set up to read input from various sources, including the user typing values on the keyboard

Keyboard input is represented by the System.in object

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The following line creates a Scanner object that reads from the keyboard

Scanner scan = new Scanner (System.in);

The new operator creates the Scanner object

Once created, the Scanner object can be used to invoke various input methods, such as

answer = scan.nextLine();

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The Scanner class is part of the java.util class library, and must be imported into a program to be used

The nextLine method reads all of the input until the end of the line is found

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Unless specified otherwise, white space is used to separate the elements (called tokens) of the input

White space includes space characters, tabs, new line characters

The next method of the Scanner class reads the next input token and returns it as a string

Methods such as nextInt and nextDouble read data of particular types

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The System.out object represents a destination (the monitor screen) to which we can send output

System.out.println ("Whatever you are, be a good one.");

object methodname

information provided to the method(parameters)

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The System.out object provides another service as well

The print method is similar to the println method, except that it does not advance to the next line

Therefore anything printed after a print statement will appear on the same line

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Java Flow of ControlJava Flow of Control

Unless specified otherwise, the order of statement execution through a method is linear: one statement after another in sequence

Some programming statements allow us to◦ decide whether or not to execute a particular

statement

◦ execute a statement over and over, repetitivelyThese decisions are based on boolean

expressions (or conditions) that evaluate to true or false

The order of statement execution is called the flow of control

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Java Flow of ControlJava Flow of Control

A conditional statement lets us choose which statement will be executed next

Therefore they are sometimes called selection statements

Conditional statements give us the power to make basic decisions

The Java conditional statements are the◦ if statement

◦ if-else statement

◦ switch statement

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Java Flow of Control - Java Flow of Control - ifif

The if statement has the following syntax

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if ( condition )

statement;

if is a Java

reserved word

The condition must be a

boolean expression. It must

evaluate to either true or false.

If the condition is true, the statement is executed.

If it is false, the statement is skipped.

Java Flow of Control - Java Flow of Control - ififAn example of an if statement:

if (sum > MAX)

delta = sum - MAX;

System.out.println ("The sum is " + sum);• First the condition is evaluated -- the

value of sum is either greater than the value of MAX, or it is not

• If the condition is true, the assignment statement is executed -- if it isn’t, it is skipped.

• Either way, the call to println is executed next

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condition

evaluated

statement

truefalse

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What do the following statements do?

if (top >= MAXIMUM)

top = 0;Sets top to zero if the current value of top is greater

than or equal to the value of MAXIMUMif (total != stock + warehouse)

inventoryError = true;

Sets a flag to true if the value of total is not equal to

the sum of stock and warehouse• The precedence of the arithmetic operators is higher than the precedence of the equality and relational operators

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Java Flow of Control – Java Flow of Control – if-elseif-else

An else clause can be added to an if statement to make an if-else statement

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if ( condition )

statement1;

else

statement2;• If the condition is true, statement1 is executed; if the condition is false, statement2 is executed

• One or the other will be executed, but not both

Java Flow of Control – Java Flow of Control – if-elseif-else

condition

evaluated

statement1

true false

statement2

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Java Flow of Control – Java Flow of Control – block block statementsstatements

Several statements can be grouped together into a block statement delimited by braces

A block statement can be used wherever a statement is called for in the Java syntax rules

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if (total > MAX)

{

System.out.println ("Error!!");

errorCount++;

}

Java Flow of Control – Java Flow of Control – block block statementsstatements

In an if-else statement, the if portion, or the else portion, or both, could be block statements

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if (total > MAX)

{

System.out.println ("Error!!");

errorCount++;

}

else

{

System.out.println ("Total: " + total);

current = total*2;

}

Java Flow of Control – Java Flow of Control – nested ifnested if

The statement executed as a result of an if statement or else clause could be another if statement

These are called nested if statements

An else clause is matched to the last unmatched if (no matter what the indentation implies)

Braces can be used to specify the if statement to which an else clause belongs

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Java Flow of Control – Java Flow of Control – switchswitch

The switch statement provides another way to decide which statement to execute next

The switch statement evaluates an expression, then attempts to match the result to one of several possible cases

Each case contains a value and a list of statements

The flow of control transfers to statement associated with the first case value that matches

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The general syntax of a switch statement is

switch ( expression )

{

case value1 :

statement-list1

case value2 :

statement-list2

case value3 :

statement-list3

case ...

}

switch

and

case

are

reserved

words

If expression

matches value2,

control jumps

to here


Often a break statement is used as the last statement in each case's statement list

A break statement causes control to transfer to the end of the switch statement

If a break statement is not used, the flow of control will continue into the next case

Sometimes this may be appropriate, but often we want to execute only the statements associated with one case


An example of a switch statementswitch (option)

{

case 'A':

aCount++;

break;

case 'B':

bCount++;

break;

case 'C':

cCount++;

break;

}


A switch statement can have an optional default case

The default case has no associated value and simply uses the reserved word default

If the default case is present, control will transfer to it if no other case value matches

If there is no default case, and no other value matches, control falls through to the statement after the switch


The expression of a switch statement must result in an integral type, meaning an integer (byte, short, int, long) or a char

It cannot be a boolean value or a floating point value (float or double)

The implicit boolean condition in a switch statement is equality

You cannot perform relational checks with a switch statement

Java Flow of Control – Repetition Java Flow of Control – Repetition StatementsStatements

Repetition statements allow us to execute a statement multiple times

Often they are referred to as loopsLike conditional statements, they are

controlled by boolean expressionsJava has three kinds of repetition

statements:◦ the while loop◦ the do loop◦ the for loop

The programmer should choose the right kind of loop for the situation

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Java Flow of Control – Java Flow of Control – whilewhile

A while statement has the following syntax

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while ( condition )

statement;

If the condition is true, the statement is executed

Then the condition is evaluated again, and if it is still true, the statement is executed again

The statement is executed repeatedly until the condition becomes false


statement

true false

condition

evaluated

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The body of a while loop eventually must make the condition false

If not, it is called an infinite loop, which will execute until the user interrupts the program

This is a common logical error

You should always double check the logic of a program to ensure that your loops will terminate normally

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Java Flow of Control – Nested LoopsJava Flow of Control – Nested Loops

Similar to nested if statements, loops can be nested as well

That is, the body of a loop can contain another loop

For each iteration of the outer loop, the inner loop iterates completely

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Java Flow of Control – Java Flow of Control – dodo

A do statement has the following syntaxdo

{

statement;

}

while ( condition )• The statement is executed once initially, and then the condition is evaluated

• The statement is executed repeatedly until the condition becomes false

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Java Flow of Control – Java Flow of Control – dodo

true

condition

evaluated

statement

false

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Java Flow of Control – Java Flow of Control – while while andand dodo

statement

true false

condition

evaluated

The while Loop

true

condition

evaluated

statement

false

The do Loop

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Java Flow of Control – Java Flow of Control – forfor

A for statement has the following syntax

for ( initialization ; condition ; increment )

statement;

The initialization

is executed once

before the loop begins

The statement is

executed until the

condition becomes false

The increment portion is executed at the

end of each iteration

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statement

true

condition

evaluated

false

increment

initialization

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A for loop is functionally equivalent to the following while loop structureinitialization;

while ( condition )

{

statement;

increment;

}

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Each expression in the header of a for loop is optional

If the initialization is left out, no initialization is performed

If the condition is left out, it is always considered to be true, and therefore creates an infinite loop

If the increment is left out, no increment operation is performed

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Java ArraysJava Arrays

A particular value in an array is referenced using the array name followed by the index in brackets

For example, the expression

scores[2]

refers to the value 94 (the 3rd value in the array)

That expression represents a place to store a single integer and can be used wherever an integer variable can be used

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For example, an array element can be assigned a value, printed, or used in a calculation

scores[2] = 89;

scores[first] = scores[first] + 2;

mean = (scores[0] + scores[1])/2;

System.out.println ("Top = " + scores[5]);

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Java ArraysJava ArraysThe values held in an array are called

array elementsAn array stores multiple values of the

same type – the element typeThe element type can be a primitive

type or an object referenceTherefore, we can create an array of

integers, an array of characters, an array of String objects, an array of Coin objects, etc.

In Java, the array itself is an object that must be instantiated

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Another way to depict the scores array

scores 79

87

94

82

67

98

87

81

74

91

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The scores array could be declared as follows

int[] scores = new int[10];

The type of the variable scores is int[] (an array of integers)

Note that the array type does not specify its size, but each object of that type has a specific size

The reference variable scores is set to a new array object that can hold 10 integers

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Some other examples of array declarations

float[] prices = new float[500];

boolean[] flags;

flags = new boolean[20];

char[] codes = new char[1750];

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Once an array is created, it has a fixed size

An index used in an array reference must specify a valid element

That is, the index value must be in range 0 to N-1

The Java interpreter throws an ArrayIndexOutOfBoundsException if an array index is out of bounds

This is called automatic bounds checking

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For example, if the array codes can hold 100 values, it can be indexed using only the numbers 0 to 99

If the value of count is 100, then the following reference will cause an exception to be thrown

System.out.println (codes[count]);

It’s common to introduce off-by-one errors when using arrays

for (int index=0; index <= 100; index++)codes[index] = index*50 + epsilon;

problem

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Each array object has a public constant called length that stores the size of the array

It is referenced using the array name

scores.length

Note that length holds the number of elements, not the largest index

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The brackets of the array type can be associated with the element type or with the name of the array

Therefore the following two declarations are equivalent

float[] prices;float prices[];

The first format generally is more readable and should be used

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An initializer list can be used to instantiate and fill an array in one step

The values are delimited by braces and separated by commas

Examples

int[] units = {147, 323, 89, 933, 540,

269, 97, 114, 298, 476};

char[] letterGrades = {'A', 'B', 'C', 'D', ’F'};

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Note that when an initializer list is used

◦ the new operator is not used

◦ no size value is specifiedThe size of the array is determined by

the number of items in the initializer list

An initializer list can be used only in the array declaration

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An entire array can be passed as a parameter to a method

Like any other object, the reference to the array is passed, making the formal and actual parameters aliases of each other

Therefore, changing an array element within the method changes the original

An individual array element can be passed to a method as well, in which case the type of the formal parameter is the same as the element type

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A one-dimensional array stores a list of elements

A two-dimensional array can be thought of as a table of elements, with rows and columns

one

dimension

two

dimensions

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Java ArraysJava ArraysTo be precise, in Java a two-dimensional

array is an array of arraysA two-dimensional array is declared by

specifying the size of each dimension separately

int[][] scores = new int[12][50];A array element is referenced using two

index valuesvalue = scores[3][6]

The array stored in one row can be specified using one index

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Expression Type Descriptiontable int[][] 2D array of integers, or

array of integer arrays

table[5] int[] array of integers

table[5][12] int integer

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An array can have many dimensions – if it has more than one dimension, it is called a multidimensional array

Each dimension subdivides the previous one into the specified number of elements

Each dimension has its own length constant

Because each dimension is an array of array references, the arrays within one dimension can be of different lengths

◦ these are sometimes called ragged arrays

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Java MethodsJava Methods

Let’s now examine method declarations in more detail

A method declaration specifies the code that will be executed when the method is invoked (called)

When a method is invoked, the flow of control jumps to the method and executes its code

When complete, the flow returns to the place where the method was called and continues

The invocation may or may not return a value, depending on how the method is defined

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myMethod();

myMethodcompute

Java MethodsJava MethodsIf the called method is in the same class,

only the method name is needed

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Java MethodsJava MethodsWe will only use static methodsA method declaration begins with a method header

static char calc (int num1, int num2, String msg)

method

name

return

type

parameter list

The parameter list specifies the type

and name of each parameter

The name of a parameter in the method

declaration is called a formal parameter

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Java MethodsJava Methods

The method header is followed by the method body

static char calc (int num1, int num2, String msg)

{

int sum = num1 + num2;

char result = msg.charAt (sum);

return result;

} The return expression

must be consistent with

the return type

sum and result

are local data

They are created each time the

method is called, and are

destroyed when it finishes

executing

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Java Methods - Java Methods - returnreturn

The return type of a method indicates the type of value that the method sends back to the calling location

A method that does not return a value has a void return type

A return statement specifies the value that will be returned

return expression;

Its expression must conform to the return type

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Java Methods – ParametersJava Methods – Parameters

When a method is called, the actual parameters in the invocation are copied into the formal parameters in the method header

char calc (int num1, int num2, String message)

{

int sum = num1 + num2;

char result = message.charAt (sum);

return result;

}

ch = obj.calc (25, count, "Hello");

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Java Methods – Local DataJava Methods – Local Data

As we’ve seen, local variables can be declared inside a method

The formal parameters of a method create automatic local variables when the method is invoked

When the method finishes, all local variables are destroyed (including the formal parameters)

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Java Class LibrariesJava Class LibrariesA class library is a collection of classes that

we can use when developing programs

The Java standard class library is part of any Java development environment

Its classes are not part of the Java language per se, but we rely on them heavily

Various classes we've already used (System , Scanner, String) are part of the Java standard class library

Other class libraries can be obtained through third party vendors, or you can create them yourself

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Java Class LibrariesJava Class Libraries

The classes of the Java standard class library are organized into packages

Some of the packages in the standard class library are

Package

java.langjava.appletjava.awtjavax.swingjava.netjava.utiljavax.xml.parsers

Purpose

General supportCreating applets for the webGraphics and graphical user interfacesAdditional graphics capabilitiesNetwork communicationUtilitiesXML document processing

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When you want to use a class from a package, you could use its fully qualified name

java.util.Scanner

Or you can import the class, and then use just the class name

import java.util.Scanner;

To import all classes in a particular package, you can use the * wildcard character

import java.util.*;

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All classes of the java.lang package are imported automatically into all programs

It's as if all programs contain the following line

import java.lang.*;

That's why we didn't have to import the System or String classes explicitly in earlier programs

The Scanner class, on the other hand, is part of the java.util package, and therefore must be imported

1001ict programming 1 semester 1, 2011 lecture 8 course review 1

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