warm-up: monday, march 3 list all devices you can think of that can be used to input information...

Warm-Up: Monday, March 3

• List all devices you can think of that can be used to input information into the computer

Warm-Up: Monday, March 3

INPUT

Pre-AP Computer ScienceCycle 5

Using Class Scanner

• Class Scanner is used to scan the computer for signals from input devices, and record inputs from these devices on your computer – Must import java.util.* library

• For our programming, the input device we’re most concerned with is the keyboard– Scan for key presses

– Record key presses as numbers, letters, strings, etc

Java Programming: Guided Learning with Early Objects 4


Input (Read) Statement

• The Scanner class puts data into variables from the standard input device– static Scanner console = new Scanner(System.in);

• Next input is: – Integer: console.nextInt()– Double: console.nextDouble()– String: console.next()or console.nextLine()


Variable Initialization

• Variable can be initialized with a literal valueint feet = 35;

• Variable can be initialized with an input statement

int feet = console.nextInt();• Variables initialized with a literal value cannot

be changed without editing the source code• Variables initialized with an input statement are

more flexible

Example A

import java.util.*;

public class Example_A

{

static Scanner console = new Scanner(System.in);

public static void main(String[ ] args)

{

System.out.println(“Enter two integers” + “separated by spaces.”);

int feet = console.nextInt();

int inches = console.nextInt();

System.out.println(“feet = “ + feet);

System.out.println(“inches = “ + inches);

}

}

Sample Run: Example A

Enter two integers separated by spaces.

23 7

feet = 23

inches = 7


import java.util.*;

public class Example_B

{



{

System.out.println(“Enter first name.”;

String firstname = console.next();

System.out.println(“Enter last name.”;

String lastname = console.next();

System.out.println(“Enter age.”);

int age = console.nextInt();

System.out.println(“Enter weight.”);

double weight = console.nextDouble();

System.out.println(“\nName: “ + firstname + “ “ + lastname);

System.out.println(“Age: “ + age);

System.out.println(“Weight: “ + weight);

}

}

Sample Run: Example B

Enter first name.

Monica

Enter last name.

Barrera

Enter age.

22

Enter weight.

126.7

Name: Monica Barrera

Age: 22

Weight: 126.7

10

Warm-Up

• What is the error in the following input statement?

double miles = console.nextInt( );


Chapter 0-1 Exam Statistics



15

Dialog Output Boxes

Chapter 2

Input/Output Review

• Used class System.out to output– System.out.print( )– System.out.println( )

• Used class Scanner to use the keyboard to provide input– Had to import the java.util.* packages– Create a new Scanner to check for keypresses

• static Scanner console = new Scanner(System.in)– Used the Scanner to accept input

• console.nextInt( ) //for integers

• console.nextDouble( ) //for doubles

• console.next( ) //for Strings 17

Review: Typical Input/Output Structureimport java.util.*

public class example

{



{

// prompt the user for what to input

// accept the input and store it in a variable

// process/manipulate the inputted information

//output the answer back to the user

}

}18

Review: Typical Input/Output Structureimport java.util.*;


{



{

System.out.println(“Enter a number.”);

int number = console.nextInt( );

int newNum = number * 3 + 6;

System.out.println(“New number = “ + newNum);

}

}19

Using Dialog Boxes

• Besides printing to the console, you can also use a generated user interface (GUI) to communicate with the user– Output AND Input

• GUI’s make the program look more user-friendly, and less like a computer program

• Closely resembles every-day computer use



Figure 2-1 Input dialog box prompting the user to input name

Creating Dialog Boxes• Dialog boxes are contained in the library

package javax.swing.*, so it must be imported at the beginning of every code

• To create an output dialog box, use the following code:

JOptionPane.showMessageDialog(null, “TEXT”, “TITLE”, JOptionPane.INFORMATION_MESSAGE);


Example Codeimport javax.swing.*;

import java.util.*;


{



{

System.out.println(“Enter a message.”);

String message = console.next( );

JOptionPane.showMessageDialog(null, message, “Your message”, JOptionPane.INFORMATION_MESSAGE);

}

}23

Example Codeimport javax.swing.*;

import java.util.*;


{



{

System.out.println(“Enter a message.”);

String message = console.next( );

JOptionPane.showMessageDialog(null, message, “Your message”, JOptionPane.INFORMATION_MESSAGE);

}

}24

Types of Messages

25

Code Template – Dialog Boxes

import javax.swing.*;

import java.util.*;

public class example {


public static void main(String[ ] args) {

//write code here

}

}

JOptionPane.showMessageDialog(null, message, “Your message”, JOptionPane.PLAIN_MESSAGE);

ERROR_MESSAGE QUESTION_MESSAGE

INFORMATION_MESSAGE

PLAIN_MESSAGE WARNING_MESSAGE 26

Warm-Up: Friday, March 7

• What is a GUI?

• When using dialog boxes, why do we need to import the javax.swing.* package?

• When you are done, TURN IN YOUR WARMUPS


Dialog Boxes - Input

Review

• Dialog boxes are pop-up boxes that can be used for input or output

• They are contained in the javax.swing.* package

• They belong to class JOptionPane


Creating Dialog Output Boxes• Dialog boxes are contained in the library

package javax.swing.*, so it must be imported at the beginning of every code

• To create an output dialog box, use the following code:

JOptionPane.showMessageDialog(null, “TEXT”, “TITLE”, JOptionPane.INFORMATION_MESSAGE);


Creating Dialog Input Boxes

• The code for input boxes is much shorter• Note: As it is input, you need to set a variable

equal to the command in order to save what the user types in

String str = JOptionPane.showInputDialog(“text”);


Example

String str;

str = JOptionPane.showInputDialog(“Enter your name and press OK”);


Dialog Input Returns Strings

• When using the dialog box for input, it always returns the input as a String, EVEN if what you’ve inputted is a number.

• That means, any number inputted into the dialog box must be converted to a number before you can use it to perform math


Converting String to Int (Parsing)

Integer.parseInt(stringName);

int number = Integer.parseInt(“56”); 56

String number = “3678”;

int Num = Integer.parseInt(number); 3678


Converting String to Float (Parsing)

Float.parseFloat(stringName);

float decimal = Float.parseFloat(“5.4”); 5.4

String number = “36.51”;

float decimal = Float.parseFloat(number); 36.51


Review

• str = JOptionPane.showInputDialog(“Enter your name and press OK”);

• int Num = Integer.parseInt(number);

• float decimal = Float.parseFloat(number);


warm-up: monday, march 3 list all devices you can think of that can be used to input information...

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