Download - Package and Some Classes Declaration of Package Usage of Package Package of Java Language
Package and Some ClassesPackage and Some ClassesPackage and Some ClassesPackage and Some Classes
Declaration of Package
Usage of Package
Package of Java Language
What is Package ?What is Package ?What is Package ?What is Package ?
Way to group a related class and interface into Way to group a related class and interface into one unit one unit
To resolve the name conflicts between class To resolve the name conflicts between class names names
Declaration of PackageDeclaration of PackageDeclaration of PackageDeclaration of Package
Declare at the beginning of source file Declare at the beginning of source file [Print1.java], [Print2.java]
package PackageName ; package PackageName ;
MyTestMyTest
PrintsPrints
Print1.classPrint1.class Print2.classPrint2.class
Usage of PackageUsage of PackageUsage of PackageUsage of Package
Use of absolute path name Use of absolute path name Declare to describe the full package name To resolve conflicts between class names
[AbsolutePath.java]
MyTest.Prints.Print1 m1; MyTest.Prints.Print2 m2;
MyTest.Prints.Print1 m1; MyTest.Prints.Print2 m2;
Use of import StatementUse of import StatementUse of import StatementUse of import Statement
Include all the classes in package Include all the classes in package import packageName.*;
[ImportTest.java]
import packageName.className ; import packageName.className ;
import MyTest.Prints.*; import MyTest.Prints.*;
java.lang Packagejava.lang Packagejava.lang Packagejava.lang Package
Basic class to enlarge the function of Java Basic class to enlarge the function of Java
Provide classes according to primitive type Provide classes according to primitive type (wrapper class)(wrapper class) Integer class, Double class,. ..
java.lang Classjava.lang Classjava.lang Classjava.lang Class
ObjectObject
NumberNumber
IntegerInteger
LongLong
FloatFloat
DoubleDouble
CharacterCharacter
SystemSystem
StringString
StringBufferStringBufferBooleanBoolean
Wrapper Class
Object ClassObject ClassObject ClassObject Class
Super class of all classes All classes are to inherit the methods of Object class Method
Object clone() : To copy the object equally boolean equals(Object obj) :
Compare the object as parameter with the object which calls this method int hashCode() : Calculate the hash code value of the object Class getClass() : To get Class object corresponding to object String toString() : Convert the object into string
[Ex 8.5] wait(), notify() : To control the status of thread
Wrapper ClassWrapper Class Wrapper ClassWrapper Class
Classes correspond to primitive type Classes correspond to primitive type int -> Integer, char -> Character, double -> Doubleint -> Integer, char -> Character, double -> Double
ReasonsReasons Role of home for constants and methods for each type When we need to deal with primitive type as object
Number ClassNumber Class Number ClassNumber Class
Abstract ClassAbstract Class Super Class of Integer, Long, Float, Double
Method abstract int intValue() : Convert into int type abstract long longValue() : Convert into long type abstract float floatValue() : Convert into float type abstract double doubleValue() : Convert into double type
Integer ClassInteger ClassInteger ClassInteger Class
ConstantConstant public static final int MAX_VALUE = 2147483647 public static final int MIN_VALUE = -2147483648
MethodMethod static int parseInt(String s) :
Convert a Number in String into int type static int parseInt(String s , int radix) :
Convert a number in String into int type with radix static String toBinaryString(int i) :
Convert into binary string form static String toHexString(int i) :
Convert into hexadecimal string form
Integer ClassInteger ClassInteger ClassInteger Class
[IntegerClass.java]
Interger.parseInt(s); Interger.toBinaryString(i); . . .
Interger.parseInt(s); Interger.toBinaryString(i); . . .
As it is staticmethod...
As it is staticmethod...
Double ClassDouble ClassDouble ClassDouble Class
ConstantConstant public static final double MAX_VALUE
=1.79769313486231570e+308 public static final double MIN_VALUE =
4.94065645841246544e-308 public static final double NaN = 0.0 / 0.0 public static final double NEGATIVE_INFINITY = -1.0 / 0.0 public static final double POSITIVE_INFINITY = 1.0 / 0.0
Double ClassDouble ClassDouble ClassDouble Class
the parameter is NaN or not. the parameter is NaN or not. static boolean isInfinite(double v) :
Check whether the parameter is infinite or not.
static Double valueOf(String s) : Method static long doubleToLongBits(double value) :
Convert the bits represented by double type into long type bit pattern
static boolean isNaN(double v) : Check whether Convert String into Double type
Boolean ClassBoolean ClassBoolean ClassBoolean Class
ConstantConstant public static final Boolean TRUE = new Boolean(true) public static final Boolean FALSE = new Boolean(false)
MethodMethod Boolean(boolean b) :
Constructor to create boolean object receiving the initial value b Boolean(String s) :
Constructor to receive the string value "true“ or "false“ boolean booleanValue() :
Return the boolean value of object static boolean getBoolean(String name) :
Return the boolean value of system attribute static Boolean valueOf(String s) :
Return the Boolean value correspond to string s
Character ClassCharacter ClassCharacter ClassCharacter Class
ConstantConstant public static final int MAX_RADIX = 36 public static final char MAX_VALUE =‘\ffff’ public static final int MIN_RADIX = 2 public static final char MIN_VALUE =’\0000’
MethodMethod Character(char value) : Constructor to initialize the object as value char charValue() : Convert into char type static boolean isDigit(char ch) : Test whether is digit? static boolean isLetter(char ch) : Test whether is letter? static boolean isLetterOrDigit(char ch) : Return when it is letter or
digit.
[CharacterClass.java]
String ClassString ClassString ClassString Class
MethodMethod char charAt(int index) :
Return the character at specific position in string
int length() : Return the length of string
String toUpperCase() : Convert the string into upper character
String toLowerCase() : Convert the string into lower character
String trim() : Remove the white space before/after string
String substring(int beginIndex) : Make the sub string from beginIndex to the end of the string
StringBuffer ClassStringBuffer ClassStringBuffer ClassStringBuffer Class
Provide the string sequence operation Provide the string sequence operation MethodMethod
StringBuffer append(Type obj) : Append the obj(to be changed into string) to string
StringBuffer insert(int offset, Type obj) : Insert obj(to be changed into string) into specified position
Object String char[] boolean char int long float double
Object String char[] boolean char int long float double
StringBuffer ClassStringBuffer ClassStringBuffer ClassStringBuffer Class
String now = new java.util.Date().toString();
StringBuffer strbuf = new StringBuffer(now);
strbuf.append(" : ").append(now.length).append('.');
System.out.println(strbuf.toString());
String now = new java.util.Date().toString();
StringBuffer strbuf = new StringBuffer(now);
strbuf.append(" : ").append(now.length).append('.');
System.out.println(strbuf.toString());
System ClassSystem ClassSystem ClassSystem Class
Class for Java Virtual Machine and the control and security for OS system
Define the standard input and output
Field public static InputStream in :
Stream to read data from standard input device
public static PrintStream out : Stream to output data to standard output device
public static PrintStream err : Standard Error Stream to output error message
Java.util.vectorJava.util.vectorJava.util.vectorJava.util.vector
We will be creating an object of Vector class and performs various operation like adding, removing etc.
Vector class extendsAbstractList and implements List, RandomAccess, Cloneable, Serializable.
The size of a vector increase and decrease according to the program.
Vector is synchronized.
Methods in VectorMethods in VectorMethods in VectorMethods in Vector
add(Object o): It adds the element in the end of the Vector
size(): It gives the number of element in the vector. elementAt(int index): It returns the element at the
specified index. firstElement(): It returns the first element of the
vector. lastElement(): It returns last element. removeElementAt(int index): It deletes the
element from the given index.
Methods in Vector classMethods in Vector classMethods in Vector classMethods in Vector class
elements(): It returns an enumeration of the element
In this example we have also used Enumeration interface to retrieve the value of a vector. Enumerationinterface has two methods.
hasMoreElements(): It checks if this enumeration contains more elements or not.
nextElement(): It checks the next element of the enumeration.
import java.util.*;public class VectorDemo{ public static void main(String[] args){ Vector<Object> vector = new Vector<Object>(); int primitiveType = 10; Integer wrapperType = new Integer(20); String str = "tapan joshi"; vector.add(primitiveType); vector.add(wrapperType); vector.add(str); vector.add(2, new Integer(30));
System.out.println("the elements of vector: " + vector);System.out.println("The size of vector are: " + vector.size());System.out.println("The elements at position 2 is: " + vector.elementAt(2));System.out.println("The first element of vector is: " + vector.firstElement());System.out.println("The last element of vector is: " + vector.lastElement());vector.removeElementAt(2);Enumeration e=vector.elements();System.out.println("The elements of vector: " + vector);while(e.hasMoreElements()){System.out.println("The elements are: " + e.nextElement());} }}
Example on Stack classExample on Stack classExample on Stack classExample on Stack class
import java.util.*;
public class StackDemo{ public static void main(String[] args) { Stack stack=new Stack(); stack.push(new Integer(10)); stack.push("a"); System.out.println("The contents of Stack is" + stack); System.out.println("The size of an Stack is" + stack.size()); System.out.println("The number poped out is" + stack.pop()); System.out.println("The number poped out is " + stack.pop()); //System.out.println("The number poped out is" + stack.pop()); System.out.println("The contents of stack is" + stack); System.out.println("The size of an stack is" + stack.size()); }}
Example on Scanner Example on Scanner classclassExample on Scanner Example on Scanner classclass
import java.util.Scanner;import java.util.Scanner;
public class ScannerDemo {public class ScannerDemo {
public static void main(String[] args) {public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);Scanner scanner = new Scanner(System.in);
// Read string input for username// Read string input for username
System.out.print("Username: ");System.out.print("Username: ");
String username = scanner.nextLine();String username = scanner.nextLine();
// Read string input for password// Read string input for password
System.out.print("Password: ");System.out.print("Password: ");
String password = scanner.nextLine();String password = scanner.nextLine();
// Read an integer input for another challenge// Read an integer input for another challenge
System.out.print("What is 2 + 2: ");System.out.print("What is 2 + 2: ");
int result = scanner.nextInt();int result = scanner.nextInt();
if (username.equals("admin") && password.equals("secret") && if (username.equals("admin") && password.equals("secret") && result == 4) {result == 4) {
System.out.println("Welcome to Java Application");System.out.println("Welcome to Java Application");
} else {} else {
System.out.println("Invalid username or password, access System.out.println("Invalid username or password, access denied!");denied!");
}}
}}
}}
Example on Date ClassExample on Date ClassExample on Date ClassExample on Date Class
import java.util.*;
public class DateDemo{ public static void main(String[] args) { Date d=new Date(); System.out.println("Today date is "+ d); }}
JAVA.IOJAVA.IO
Example on FileExample on FileExample on FileExample on File
import java.io.*;class FileWrite { public static void main(String args[]) { try{ // Create file FileWriter fstream = new FileWriter("out.txt",true); BufferedWriter out = new BufferedWriter(fstream); out.write("Hello Java"); //Close the output stream out.close(); }catch (Exception e){//Catch exception if any System.err.println("Error: " + e.getMessage()); } }}
java.io.Reader classjava.io.Reader class
BufferedReader classBufferedReader class
Method Return Type
Description
read( ) int Reads a single character
read(char[] cbuf, int off, int len)
int Read characters into a portion of an array.
readLine( ) String Read a line of text. A line is considered to be terminated by ('\n').
close( ) void Closes the opened stream.
import java.io.*; public class ReadStandardIO{ public static void main(String[] args) throws IOException{
InputStreamReader inp = new InputStreamReader(System.in) BufferedReader br = new BufferedReader(inp);
System.out.println("Enter text : "); String str = in.readLine();
System.out.println("You entered String : ");
System.out.println(str); }}