Decision Making Statements

A java program has many statements, these statements are executed sequentially.
If a program has two or more conditions and user want to perform a particular condition which satisfy user's need, then Decision Making concept is used.

JAVA has some following Decision Making Statements:
  • IF statements
  • switch statements


if statements: if statements are used to check the condition in true or false.

  • Simple if statement
  • if-else statement
  • if-else-if ladder
  • Nested if


Simple if: If condition is true then particular statement block will be executed otherwise skipped.

syntax:
if(condition){
                //block of statement;
}

Program:
public class Eligibility{
          public static void main(String[] args){
                        int age = 19;
                        if(age > 18){
                                    System.out.println("Person is eligible");
                        }
          }
}


if-else: In this statement if condition is followed by an else condition. If condition is true if block will be executed otherwise false block executed.

syntax:
if(condition){
                //true statement block;
}
else{
                //false statement block;
}

Program: 
public class Number{
          public static void main(String[] args){
                    int num = 22;
                     if(num % 2 == 0){                                                                              System.out.println("Number is even");
                     }
                     else{
                           System.out.println("Number is odd");
                     }
         }
}

if-else-if ladder: It is used when there is multiple choices. if-else-if ladder has one if then else if statement and so on.

syntax:
if(condition 1){
                //condition 1 statement block;
}
else if(condition 2){
                //condition 2 statement block;
}
else if(condition 3){
                //condition 3 statement block;
}
else{
                //when all conditions are false
}


Program:
class Result{
          public static void main(String[] args){
                          int marks = 67;
                          if(marks >= 65){
                                        System.out.println("Grade A");
                          }
                          else if(marks >= 50){
                                        System.out.println("Grade B");
                          }
                          else(marks > 35){
                                        System.out.println("Grade C");
                          }
          }
}

nested if: In nested if statements there can be one or more if statements within if statement.

syntax:
if(condition1){
                if(condition 2){
                                //both conditions are true;
                }
                else{
                                //condition1 is true;
                }
}
else{
                //No condition satisfy;
}


Program:
class Person{
          public static void main(String[] args){
                     int age = 20;
                     char sex = 'f';
                     if(sex == 'm'){
                           if(age >= 21){
                                   System.out.println("Person is eligible");
                           }
                           else{
                                  System.out.println("Person is not eligible");
                           }
                     }
                      else{
                              if(sex == 'f'){
                                   if(age >= 18){
                                         System.out.println("Person is eligible");
                                   }
                                    else{
                                           System.out.println("Person is not eligible");
                                           }
                                   }
                     }
         }
}

               

Switch Statements: Switch Statement is used to perform equality operation. When there is multiple choices for if then using equality operation switch is used.

syntax:
switch(expression){
                case 1:
                                //statements
                break;
                case 2:
                                //statements
                break;
                .
                .
                .
                default:
                                //statements
}


Program:
class Number;
{
          public static void main(String[] args){
                     int value = 3;
                      switch(value){
                                case 1:
                                         System.out.println("Value is 1");
                                 break;
                                case 2:
                                         System.out.println("Value is 2");
                                 break;
                                case 3:
                                         System.out.println("Value is 3");
                                 break;
                                 defalut:
                                         System.out.println("Wrong choice");
                     }
         }
}



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