The If-Else If Statement, Nested If Statements, Logical Operators

• In a decision structure’s simplest form certain statements are executed only when…
  • a specific condition exists.
• It is said that the statements inside of the decision structure are…
  • conditionally executed.
• Relational Operators determine whether…
  • a specific relationship exist between two values.
• Some relational operators in Java are…
  • > , < , >= , <= , == , !=

• General for of an if statement:

if(BooleanExpression)

statement;

if(BooleanExpression) {

statement1;

statement2;

...

}

• A Flag is…
  • a boolean variable that signals when some condition exists in a program.
• When Java compares characters, it compares the character’s…
  • Unicode values

Review

• General form of an if-else statement:

if(BooleanExpression)

statement or block 1

else

statement or block 2

The if-else if Statement

• Sometimes you need to be able to test a series of conditions
  • You can do this with the if-else if statement
• General form:

if (BooleanExpression1)

statement or block 1

if else (BooleanExpression2)

statement or block 2

else

statement or block 3

• If BooleanExpression1 is true, then statement or block 1 is executed.
• If BooleanExpression1 is false, then BooleanExpression2 is tested.
  • If BooleanExpression2 is true, then statement or block 2 is executed.
  • If BooleanExpression2 is false, then statement or block 3 is executed.
• Note: You can have as many if else clauses as is needed.

if-else if Example

• New Topics:
  • if-else if Statement
  • Using else as an error case

Nested if Statements

• Nesting is enclosing one structure inside of another.
  • A block in Java can contain any valid Java code, this includes other if statements:

if(BooleanExpression1) {

if(BooleanExpression2) {

statement1;

statement2;

}

statement3;

statement4;

}

• If BooleanExpression1 is true and BooleanExpression2 is true , what is executed?
  • statement1 , statement2 , statement3 , statement4
• If BooleanExpression1 is true and BooleanExpression2 is false , what is executed?
  • statement3 , statement4
• If BooleanExpression1 is false, what is executed?
  • Nothing

Nested if Statements Example

• New Topics:
  • Nested if Statements

Logical Operators

• Java provides logical operators.
  • The binary logical operators combine two boolean expressions into one.
  • The unary logical operator switches the value of a boolean expression.

• Binary logical operators have lower precedence than relational operators (they will be evaluated after)
• NOT has the same precedence as negation.

 

Operator	Meaning	Kind
&&	AND	Binary
||	OR	Binary
!	NOT	Unary

Logical Operator Truth Tables

• Truth Tables show the result of a logical expression based on the values of the operands.

 

 

 

Logical Operator Practice

• 2 > 3 && 4 < 5
  • false – first operand is false
• 2 < 3 && 4 < 5
  • true
• 2 > 3 || 4 < 5
  • true
• 2 > 3 || 4 > 5
  • false – both operands are false
• !(2 > 3)
  • true – operand is false

Logical AND Example

• New Topics:
  • Logical AND

Logical AND and Nesting

• If we have the && operator, do we need nesting?

if(BooleanExpression1) {

if(BooleanExpression2) {

Both conditions met

}

else {

Both conditions NOT met

}

}

else {

Both conditions NOT met

}

if(BooleanExpression1 && BooleanExpression2) {

Both conditions met

}

else {

Both conditions NOT met

}

Logical AND and Nesting

• Answer: Yes, to act if one of the conditions is not met:

if(BooleanExpression1) {

if(BooleanExpression2) {

Both conditions met

}

else {

Condition 2 not met

}

}

else {

Condition 1 not met

}
if(BooleanExpression1 && BooleanExpression2) {

Both conditions met

}

else {

Both conditions NOT met

}

Example :

/*************************************************************************
 * IF ... ELSE Statements and Relational Operators Example
 *
 *************************************************************************/

public class MyClass {
	/*
     == is equal to
     != is not equal to
     > is greater than
     < is less than
     >= is greater than or equal to
     <= is less than or equal to
	 */
	public static void main(String[] args) {
		int x = 10;
		if (x <= 20) {
			System.out.println("yes x == 10");
		}
		else {
			System.out.println("no x != 10");
		}
	}
}