Decision Making in Java - Conditional Statements

Decision-making in programming is similar to real-life decision-making. We often want certain blocks of code to execute only when specific conditions are met. In Java, this is achieved using decision-making statements that control the flow of execution.

In Java, the following decision-making statements are available:

Java if Statement

The if statement is the simplest decision-making statement. It executes a block of code only if a given condition is true.

class Geeks {
    public static void main(String args[])
    {
        int i = 10;

        if (i < 15) {
            System.out.println("Condition is True");
        }
    }
}

Condition is True

Note: If curly braces {} are omitted, only the next line after if is considered part of the block.

if Statement Execution Flow

The below diagram demonstrates the flow chart of an "if Statement execution flow" in programming.

Java if-else Statement

The if-else statement allows you to execute one block if the condition is true and another block if it is false.

import java.util.*;

class Geeks {
    public static void main(String args[])
    {
        int i = 10;

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

i is smaller than 15

if-else Statement Execution flow

The below diagram demonstrates the flow chart of an "if-else Statement execution flow" in programming

Java nested-if Statement

A nested-if is an if statement inside another if statement. It is useful when a second condition depends on the first.

class Geeks {
    public static void main(String args[])
    {
        int i = 10;

        // Outer if statement
        if (i < 15) {
            System.out.println("i is smaller than 15");

            // Nested if statement
            if (i == 10) {
                System.out.println("i is exactly 10");
            }
        }
    }
}

i is smaller than 15
i is exactly 10

nested-if Statement Execution Flow

The below diagram demonstrates the flow chart of an "nested-if Statement execution flow" in programming.

Java if-else-if ladder

The if-else-if ladder allows multiple independent conditions to be checked in order. As soon as one condition is true, its block executes, and the rest are skipped.

import java.util.*;

class Geeks {
    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");
    }
}

i is 20

if-else-if ladder Execution Flow

The below diagram demonstrates the flow chart of an "if-else-if ladder execution flow" in programming

Java 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. 

import java.io.*;

class Geeks {
    public static void main(String[] args)
    {
        int num = 20;
        switch (num) {
        case 5:
            System.out.println("It is 5");
            break;
        case 10:
            System.out.println("It is 10");
            break;
        case 15:
            System.out.println("It is 15");
            break;
        case 20:
            System.out.println("It is 20");
            break;
        default:
            System.out.println("Not present");
        }
    }
}

It is 20

switch Statements Execution Flow

The below diagram demonstrates the flow chart of a "switch Statements execution flow" in programming.

Note:

• The expression can be of type byte, short, int char, or an enumeration. Beginning with JDK7, the 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 statements are necessary without the break keyword, statements in switch blocks fall through.  

Ternary Operator (? :) in Java

The ternary operator in Java is a conditional operator that provides a shorthand way to write simple if-else statements

Syntax:

condition ? expression_if_true : expression_if_false;

class Geeks {
    public static void main(String args[]) {
        int a = 10, b = 20;
        int max = (a > b) ? a : b;

        System.out.println("Maximum is " + max);
    }
}

Maximum is 20

Explanation: This program uses the ternary operator ( ? : ) to find the maximum of two numbers. It checks the condition a > b; if true, it assigns a to the variable max, otherwise it assigns b. Finally, it prints the maximum value.

if-else vs switch-case

The table below demonstrates the difference between if-else and switch-case.