java 03 dse part2

7/28/2019 Java 03 DSE Part2

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Chapter 3 Control Statements

Selection StatementsUsing if and if...else

Nested if Statements

Using switch Statements

Conditional Operator

Repetition Statements

Looping: while, do-while,and for

Nested loops

Using break and continue


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Repetitions

while Loops

do-while Loops

for Loops

break and continue


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while Loop Flow Chart

false

true

Statement(s)

Next

Statement

Continuation

condition?

while (continuation-condition) {// loop-body;

}


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while Loop Flow Chart, cont.

int i = 0;while (i < 100) {System.out.println("Welcome to Java!");

i++;}

false

true

System.out.println("Welcoem to Java!");

i++;

NextStatement

(i < 100)

i = 0;


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Example 3.2: Using while Loops// TestWhile.java: Test the while loop

import javax.swing.JOptionPane;

public class TestWhile {

/** Main method */

public static void main(String[] args) {

int data;

int sum = 0;

// Read an initial data

String dataString = JOptionPane.showInputDialog(null,

"Enter an int value, \nthe program exits if the input is 0",

"Example 3.2 Input", JOptionPane.QUESTION_MESSAGE);

data = Integer.parseInt(dataString);

// Keep reading data until the input is 0

while (data != 0) {

sum += data;

// Read the next data

dataString = JOptionPane.showInputDialog(null,

"Enter an int value, \nthe program exits if the input is 0",

"Example 3.2 Input", JOptionPane.QUESTION_MESSAGE);

data = Integer.parseInt(dataString);

}

JOptionPane.showMessageDialog(null, "The sum is " + sum,

"Example 3.2 Output", JOptionPane.INFORMATION_MESSAGE);

System.exit(0);

}

}


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Caution

Dont use floating-point values for equality checking in a

loop control. Since floating-point values areapproximations, using them could result in imprecise

counter values and inaccurate results. This example uses

int value for data. If a floating-point type value is used for

data, (data != 0) may be true even though data is 0.

// data should be zero

double data = Math.pow(Math.sqrt(2), 2) - 2;

if (data == 0)

System.out.println("data is zero");

else

System.out.println("data is not zero");


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do-while Loop

false

true

Statement(s)

Next

Statement

Continue

condition?

do {

// Loop body;

} while (continue-condition);


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for Loopsfor (initial-action; loop-continuation-condition;

action-after-each-iteration) {//loop body;

}

int i = 0;

while (i < 100) {

System.out.println("Welcome to Java! + i);

i++;

}

Example:

int i;for (i = 0; i < 100; i++) {

System.out.println("Welcome to Java! + i);

}


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for Loop Flow Chart

Initial-Action

false

true

Action-After-

Each-Iteration

Statement(s)

(loop-body)

Next

Statement

Continuation

condition?

for (initial-action;loop-continuation-condition;action-after-each-iteration) {//loop body;

}


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for Loop Example

i


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Which Loop to Use?

The three forms of loop statements, while, do, and for, are

expressively equivalent; that is, you can write a loop in

any of these three forms.

I recommend that you use the one that is most intuitive

and comfortable for you. In general, a for loop may beused if the number of repetitions is known, as, for

example, when you need to print a message 100 times. A

while loop may be used if the number of repetitions is not

known, as in the case of reading the numbers until the

input is 0. A do-while loop can be used to replace a while

loop if the loop body has to be executed before testing the

continuation condition.


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Caution

Adding a semicolon at the end of the for clause

before the loop body is a common mistake, as

shown below:

for (int i=0; i


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Caution, cont.Similarly, the following loop is also wrong:int i=0;while (i


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The break Keyword

false

true

Statement(s)

Next

Statement

Continuation

condition?

Statement(s)

break


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The continue Keyword

false

true

Statement(s)

Next

Statement

Continue

condition?

Statement(s)

continue


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Using breakExample for using the break keyword: 3.5

// TestBreak.java: Test the break keyword in the loop

public class TestBreak {

/** Main method */


int sum = 0;

int item = 0;

while (item < 5) {

item ++;

sum += item;

//if (sum >= 6) break;

}

System.out.println("The sum is " + sum);

}

}


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Using continueExample for using the continue keyword:

// TestContinue.java: Test the continue keywordpublic class TestContinue {

/** Main method */


int sum = 0;

int item = 0;

while (item < 5) {

item++;

if (item == 2) continue;

sum += item;

}

System.out.println("The sum is " + sum);

}

}


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Review of Terms: Deenas Class

The 3 essential elements of a programming loop:

priming, test, and update

User-controlled loops vs Program-controlled loops

Some user-controlled loops usesentinels.

AccumulatorandMarkervariables: how are these

used in loops?

What is aflagvariable? When do you use it?

java 03 dse part2

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