Control Flow Statements in Java

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In Java there are three types of control flow statements:

1. Decision making statements: if, if else, nested if else
2. Looping statements: while, for, do-while
3. Branching statements: return, break, continue

if statement

It instructs the program to execute only certain part of the code if the condition is true.
If boolean value is true then statement1 will be executed.

Syntax:

if (boolean expr)
{
statement 1: //expr true
}
statement 2;

Flow Diagram

Fig: Flow diagram of if statement

if else statement

In this case, when if clause is false then else part will be executed.

Syntax:

if (boolean expr)
{
statement 1; //expr true
}
else
{
statement 2; //expr false
}

Flow Diagram
if else

Fig: Flow diagram of if else statement

Nested if else

Syntax:

if (boolean expr1)
{
     statement 1;      // expr1 true
}
else if (boolean expr2)
{
     Statement 2;      // expr 1 false and expr 2 true
}
else
{
     statement 3;      // expr 2 false
}

Example: Program for nested if else statement

Program to find largest number of three given numbers using if else.

class Test
{
     public static void main(String args[])
     {
          int x = 20;
          int y = 15;
          int z = 30;
          if (x > y)
          {
               if (x > z)
                    System.out.println("Largest number is: "+x);
               else
                    System.out.println("Largest number is: "+z);
          }
          else
          {
               if (y > z)
                    System.out.println("Largest number is: "+y);
               else
                    System.out.println("Largest number is: "+z);
          }
     }
}

Output:
Largest number is: 30

Switch Case Statement

It is type of selection mechanism that provides multi-way selection.

Flow Diagram

switch

Fig: Flow diagram of switch statement

Example: Simple program of switch statement

class SwitchDemo
{
     public static void main(String[] args)
     {
          int day = 6;
          String dayString;
          switch (day)
          {
               case 1:  dayString = "Sunday";
               break;
               case 2:  dayString = "Monday";
               break;
               case 3:  dayString = "Tuesday";
               break;
               case 4:  dayString = "Wednesday";
               break;
               case 5:  dayString = "Thursday";
               break;
               case 6:  dayString = "Friday";
               break;
               case 7:  dayString = "Saturday";
               break;
               default: dayString = "Invalid day";
               break;
          }
          System.out.println (dayString);
     }
}

Output:
Friday