Relational Operators Control structures Decisions using “if” statements 2000 Prentice Hall,...
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![Page 1: Relational Operators Control structures Decisions using “if” statements 2000 Prentice Hall, Inc. All rights reserved. Modified for use with this course.](https://reader036.fdocuments.in/reader036/viewer/2022062516/56649d6a5503460f94a47e3b/html5/thumbnails/1.jpg)
Relational OperatorsControl structures
Decisions using “if” statements
2000 Prentice Hall, Inc. All rights reserved. Modified for use with this course.
Introduction to Computers and Programming in JAVA: V22.0002
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2000 Prentice Hall, Inc. All rights reserved.
Displaying Text in a Dialog Box
• Display– Most Java applications use windows or a dialog box
• We have used command window
– Class JOptionPane allows us to use dialog boxes
• Packages– Set of predefined classes for us to use
– Groups of related classes called packages• Group of all packages known as Java class library or Java
applications programming interface (Java API)
– JOptionPane is in the javax.swing package• Package has classes for using Graphical User Interfaces
(GUIs)
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2000 Prentice Hall, Inc. All rights reserved.
Review Packages in Java
– Two groups of packages in Java API
– Core packages• Begin with java
• Included with Java 2 Software Development Kit
– Extension packages• Begin with javax
– import declarations • Used by compiler to identify and locate classes used in Java
programs
• Tells compiler to load class JOptionPane from javax.swing package
4 // Java packages
5 import javax.swing.JOptionPane; // program uses OptionPane
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2000 Prentice Hall, Inc. All rights reserved.
// InputDataDemo.java: Entering input from input dialog boxes. Finding the square of a number
import javax.swing.JOptionPane;
public class Class5_Input_DataDemo {
public static void main(String args[]) {
int result; // declare the result
// Prompt the user to enter a number:
String numString = JOptionPane.showInputDialog(null,
"Enter a number from 1 to 10:", "Input Window Demo", JOptionPane.QUESTION_MESSAGE);
// Convert the string into an int value
int num = Integer.parseInt(numString);
result = num * num ;
// Display the result in a message dialog box
JOptionPane.showMessageDialog(null,
num + " squared is " + result, "Input Window Demo", JOptionPane.INFORMATION_MESSAGE);
System.exit(0);
}
}
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2000 Prentice Hall, Inc. All rights reserved.
Three Basic Control Structures
• All programs can be written with just these types of structures– Sequence structure
• Statements run one after the other
– Selection structure• Depending on a condition, do one thing (single selection using if); • otherwise, do something else (Double selection using if else)• if, if-else, and switch (multiple selections).
– Repetition structure• Repeat some actions over and over• for loops, while loops, and do/while loops.
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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Flow Chart Basics 1
Rectangles represent statements of work. For example:
print()
Diamonds(decision symbol)
contain conditions flow
line
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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Flow Chart Basics Sequence structure
Connector symbol
Triangle boxes represent statements
such as
x=30;
int a;
System.out.print(“x”);
x=20;
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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Decision Making: Equality and Relational Operators
• if control statement– If a condition is true, then the body of the if statement gets
executed
– Control always resumes after the if structure
if ( condition ) statement executed if condition
true
• No semicolon needed after condition
– Else: otherwise the conditional task is not performed
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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The if structure
• If some condition is true– do this
• Example:if ( x == y ) {
System.out.println(“ x is equal to y!\n” ) ; }
• Every programming language has some form of an if statement.
• Note the operator: = vs ==
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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Flow Chart Basics Selection structure Single selection (if)
print “passed”grade >=60true
Connector symbol
false
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Equality and Relational Operators
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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The if structure• If some condition is true
– do this– else, do something else
• Example:if ( x == y )
{
System.out.println(“ x is equal to y!\n“ ) ; }
else
{
System.out.println(“ x is NOT equal to y!\n“);}
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2000 Prentice Hall, Inc. All rights reserved.
if/else Flow Chart
grade >=60
Print “You passed”
Print “You failed”
TrueFalse
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2000 Prentice Hall, Inc. All rights reserved.
Even Odd program
• Lets write a program in class that will:– input a number between 1-10
– test whether a number is even or odd
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2000 Prentice Hall, Inc. All rights reserved.
Even or Odd numbers
// even & odd numbers: using "mod" import javax.swing.JOptionPane;
public class even_odd { public static void main(String args[]) {
// Prompt the user to enter a number:
String numString = JOptionPane.showInputDialog(null, "Enter a number from 1 to 10:", "Input Window Demo", JOptionPane.QUESTION_MESSAGE); // Convert the string into an int value
int num = Integer.parseInt(numString);
// Display the result in a message dialog box
if ( ( num % 2 ) == 0 )System.out.println(" The number " + num + " is even.");
elseSystem.out.println(" The number " + num + " is odd.");
System.exit(0); } }
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2003 Prentice Hall, Inc.All rights reserved.
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Comparison.java
1. import
2. Class Comparison
2.1 main
2.2 Declarations
2.3 Input data (showInputDialog)
2.4 parseInt
2.5 Initialize result
1 // Comparison.java2 // Compare integers using if statements, relational operators 3 // and equality operators.4 5 // Java packages6 import javax.swing.JOptionPane;7 8 public class Comparison {9 10 // main method begins execution of Java application11 public static void main( String args[] )12 {13 String firstNumber; // first string entered by user14 String secondNumber; // second string entered by user15 String result; // a string containing the output16 17 int number1; // first number to compare18 int number2; // second number to compare19 20 // read first number from user as a string21 firstNumber = JOptionPane.showInputDialog( "Enter first integer:" );22 23 // read second number from user as a string24 secondNumber =25 JOptionPane.showInputDialog( "Enter second integer:" );26 27 // convert numbers from type String to type int28 number1 = Integer.parseInt( firstNumber );29 number2 = Integer.parseInt( secondNumber );30 31 // initialize result to empty String32 result = ""; 33
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2003 Prentice Hall, Inc.All rights reserved.
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Comparison.java
3. if statements
4. showMessageDialog
34 if ( number1 == number2 ) 35 result = result + number1 + " == " + number2;36 37 if ( number1 != number2 ) 38 result = result + number1 + " != " + number2;39 40 if ( number1 < number2 ) 41 result = result + "\n" + number1 + " < " + number2;42 43 if ( number1 > number2 ) 44 result = result + "\n" + number1 + " > " + number2;45 46 if ( number1 <= number2 ) 47 result = result + "\n" + number1 + " <= " + number2;48 49 if ( number1 >= number2 ) 50 result = result + "\n" + number1 + " >= " + number2;51 52 // Display results 53 JOptionPane.showMessageDialog( null, result, "Comparison Results",54 JOptionPane.INFORMATION_MESSAGE ); 55 56 System.exit( 0 ); // terminate application57 58 } // end method main59 60 } // end class Comparison
Test for equality, create new string, assign to result.
Notice use of JOptionPane.INFORMATION_MESSAGE
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Program Output
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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2.8 Decision Making: Equality and Relational Operators
– Lines 1-12: Comments, import JOptionPane, begin class Comparison and main
– Lines 13-18: declare variables• Can use comma-separated lists instead:
– Lines 21-30: obtain user-input numbers and parses input string into integer variables
13 String firstNumber, 14 secondNumber, 15 result;
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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2.8 Decision Making: Equality and Relational Operators
– Initialize result with empty string
– if statement to test for equality using (==)• If variables equal (condition true)
– result concatenated using + operator
– result = result + other strings– Right side evaluated first, new string assigned to result
• If variables not equal, statement skipped
32 result = "";
34 if ( number1 == number2 ) 35 result = result + number1 + " == " + number2;
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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2.8 Decision Making: Equality and Relational Operators
– Lines 37-50: other if statements testing for less than, more than, etc.
• If number1 = 123 and number2 = 123
– Line 34 evaluates true (if number1 = = number 2)
• Because number1 equals number2
– Line 40 evaluates false (if number1 < number 2)
• Because number1 is not less than number2
– Line 49 evaluates true (if number1 >= number2)
• Because number1 is greater than or equal to number2
– Lines 53-54: result displayed in a dialog box using showMessageDialog
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2003 Prentice Hall, Inc. All rights reserved (Modified) .
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2.8 Decision Making: Equality and Relational Operators
• Precedence of operators– All operators except for = (assignment) associates from left
to right• For example: x = y = z is evaluated x = (y = z)
Operators Associativity Type * / % left to right multiplicative + - left to right additive < <= > >= left to right relational == != left to right equality = right to left assignment Fig. 2.21 Precedence and associativity of the operators discuss ed so far.
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2000 Prentice Hall, Inc. All rights reserved.
• Lets write a program in class:– Write a program that will input a number
from 1-10 (using input dialog box)
– Determine if the number entered is equal to 5
– OR less than 5
– Or larger than 5
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2000 Prentice Hall, Inc. All rights reserved.
// less than five!!import javax.swing.JOptionPane;
public class less_than_5{ public static void main(String args[]) {
// Prompt the user to enter a number: String numString = JOptionPane.showInputDialog(null, "Enter a number from 1 to 10:", "Input Window Demo", JOptionPane.QUESTION_MESSAGE); // Convert the string into an int value int num = Integer.parseInt(numString);
// Display the result in a message dialog boxif ( num < 5 )
System.out.println(" The number " + num + " is less than five.");else
if (num == 5) System.out.println(" The number " + num + " is equal to five.");
else System.out.println(" The number " + num + " is greater than five.");
System.exit(0); } }