Introduction to Computing ConceptsNote Set 15

JOptionPane.showMessageDialog•Message Dialog•Allows you to give a brief message to the user

•Can be used to give helpful messages, errors, or warnings.

Example

import javax.swing.JOptionPane;

public class Tester {

public static void main (String [] args) {

JOptionPane.showMessageDialog(null, "Hello There!!!");

}

}

JOptionPane.showInputDialog•Pops up a dialog and allows the user to enter a string•Method returns a string

•Can be used to ask for strings or numbers.▫Must convert string version of number to numerical

type

Example

import javax.swing.JOptionPane;

public class Tester { public static void main (String [] args) { String data; data = JOptionPane.showInputDialog(null,

"Please input your name."); System.out.println("Hello“ + data); }}

•Use JOptionPane to get 5 numbers from the user then display to the screen.

public static void main(String [] args) {

Breakout 1

do…while Loop

do //some Java Statementwhile (expression);

do { //some //statements //can go here} while (expression);

single statementno braces

multiple statementsneed braces

Two Types of Loops

do { //some //statements //can go here} while (expression);

VS:

while(expression) { //do something //here}

What is Displayed

int x = 1;while (x < 0) System.out.println(x);

do System.out.println(x);while (x < 0);

What is Displayed?

int c = 10;do { System.out.println(“hello”); c++;} while (c < 4);

What is Displayed?

int v = 0;do { v++; System.out.println(v); } while (v < 4);

What is Displayed?int count = 0;int funny = 1;int serious = 0;int limit = 4;do { funny ++; serious = serious + 2; count = count + 1;} while (count < limit);System.out.println(funny + “ “ + serious + “ “ + count );

QuickCode•Write a snippet of code that asks the user to enter

integers until the sum of the numbers entered is greater than 300. Use a do…while loop

Nested Loops• It is possible to have one looping structure inside

another

int first = 0;int second = 0;while (first < 3) { do { System.out.print(“*”); //doesn’t go to next line second += 1; }while (second < 4); System.out.println(); first += 1; second = 0;}

Breakout 2

17

For Loop

• Ideal for situations that require a counter

•Has built in expressions that initialize and update variables

18

For Loop

for (initialization; test; update)

statement;

for (initialization; test; update){

statement;statement;//Place as many here as needed

}

19

For Loop

for (initialization; test; update)

statement;

Used to set up counter variable

20

For Loop

for (initialization; test; update)

statement;

Controls execution of loop

21

For Loop

for (initialization; test; update)

statement;

Updates (increments) counter variable

22

For Loop

for (int num=0; num<4; num++)

System.out.println(num + “\t” + num*num);

1. Perform initialization of counter

23

for (int num=0; num<4; num++)

System.out.println(num + “\t” + num*num);

For Loop

1. Perform initialization of counter

2. Evaluate test

• if num < 4, go to step 3

• else terminate loop

24

for (int num=0; num<4; num++)

System.out.println(num + “\t” + num*num);

For Loop

1. Perform initialization of counter

2. Evaluate test

3. Execute statement

25

for (int num=0; num<4; num++)

System.out.println(num + “\t” + num*num);

For Loop

1. Perform initialization of counter

2. Evaluate test

3. Execute statement

4. Perform update – go back to step 2