Decision Making Statements

• Decision Making in programming is similar to decision making in real life. 
• A programming language uses control statements to control the flow of execution of program based on certain conditions. 
• These are used to cause the flow of execution to advance and branch based on changes to the state of a program.
• A. if
• Syntax:

if(condition)
{

}

• Here, condition after evaluation will be either true or false.
• Example:

class IfDemo
{
    public static void main(String args[])
    {
        int i = 11;

        if (i > 12)
            System.out.println("11 is less than 12");

        System.out.println("I am Not in if");
    }
}

• B. if-else
• The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. 
• We can use the else statement with if statement to execute a block of code when the condition is false.
• Syntax:

if (condition)
{
    // Executes this block if
    // condition is true
}
else
{
    // Executes this block if
    // condition is false
}

• Example:

class IfElseDemo
{
    public static void main(String args[])
    {
        int i = 11;

        if (i < 12)
            System.out.println("11 is smaller than 12");
        else
            System.out.println("12 is greater than 11");
    }
}

• C. nested-if
• A nested if is an if statement that is the target of another if or else. 
• Nested if statements means an if statement inside an if statement. 
• Syntax:

if (condition1)
{
   // Executes when condition1 is true
   if (condition2)
   {
      // Executes when condition2 is true
   }
}

• Example:

class NestedIfDemo
{
    public static void main(String args[])
    {
        int i = 11;

        if (i == 11)
        {
            // First if statement
            if (i < 12)
                System.out.println("11 is smaller than 12");

            if (i < 15)
                System.out.println("11 is smaller than 15 too");
            else
                System.out.println("15 is greater than 11");
        }
    }
}

• D. if-else-if ladder:
• The if statements are executed from the top down. 
• As soon as one of the conditions controlling the if is true, the statement associated with that if is executed. 
• If none of the conditions is true, then the final else statement will be executed.
• Syntax:

if (condition)
    statement;
else if (condition)
    statement;
.
.
else
    statement;

• Example:

class ifelseifDemo
{
    public static void main(String args[])
    {
        int i = 20;

        if (i == 10)
            System.out.println("i is 10");
        else if (i == 15)
            System.out.println("i is 15");
        else if (i == 20)
            System.out.println("i is 20");
        else
            System.out.println("i is not present");
    }
}

• E. switch-case
• The switch statement is a multiway branch statement. 
• It provides an easy way to dispatch execution to different parts of code based on the value of the expression.
• Syntax:

switch (expression)
{
  case value1:
    statement1;
    break;
  case value2:
    statement2;
    break;
  .
  .
  case valueN:
    statementN;
    break;
  default:
    statementDefault;
}

• Expression can be of type byte, short, int char or an enumeration. 
• Note: Beginning with JDK7, expression can also be of type String.
• Duplicate case values are not allowed.
• The default statement is optional.
• The break statement is used inside the switch to terminate a statement sequence.
• The break statement is optional. If omitted, execution will continue on into the next case.
• Example:

class SwitchCaseDemo
{
    public static void main(String args[])
    {
        int i = 9;
        switch (i)
        {
        case 0:
            System.out.println("i is zero.");
            break;
        case 1:
            System.out.println("i is one.");
            break;
        case 2:
            System.out.println("i is two.");
            break;
        default:
            System.out.println("i is greater than 2.");
        }
    }
}

• F. jump – break, continue, return
• Java supports three jump statement: break, continue and return.
• 1. Break: In Java, break is majorly used for:
• Terminate a sequence in a switch statement (discussed above).
• To exit a loop.
• Syntax: break;
• Example:

class BreakLoopDemo
{
    public static void main(String args[])
    {
        // Initially loop is set to run from 0-9
        for (int i = 0; i < 10; i++)
        {
            // terminate loop when i is 5.
            if (i == 5)
                break;

            System.out.println("i: " + i);
        }
        System.out.println("Loop complete.");
    }
}

• 2. Continue
• It is used to continue running the loop but stop processing as per condition.
• Syntax: Continue;
• Example:

class ContinueDemo
{
    public static void main(String args[])
    {
        for (int i = 0; i < 10; i++)
        {
            // If the number is even
            // skip and continue
            if (i%2 == 0)
                continue;

            // If number is odd, print it
            System.out.print(i + " ");
        }
    }
}

• 3. Return:
• The return statement is used to explicitly return from a method. 
• That is, it causes program control to transfer back to the caller of the method.
• Syntax: return;
• Example:

class Return
{
    public static void main(String args[])
    {
        boolean t = true;
        System.out.println("Before the return.");
   
        if (t)
            return;

        System.out.println("This won't execute.");
    }
}