If, If Else, nested Condition - Statement in java with Examples

If Statement in java 

In this post, We will discuss about If statement, If Else, Multiple if-else, nested Statement or condition in java with examples.

We will learn

1. If statement
2. If-Else statement
3. Multiple if else statement
4. Nested if else statement

Java If Statement:

This is very basic topic in every programming language and simple to learn, use it in your programs.
First we see the syntax of If Statement.

Mainly If condition is for:

If one specific condition is true then do execution of set of statement. If not, skip specified statements.

If Statement Syntax:

if(expression)
{
   // Executes the code here if expression returns true.
}

Expression evaluation should be boolean.
If expression evaluation is true then code will be executed inside block.
If expression evaluation is false then code will not be executed.

This is very useful in cases where we want to execute a set of statements on a condition basis.

if (true) then
    execute set of statements
end if.

The following flow chart depicts the way if condition works.

Valid Example:

package com.adeepdrive.statement;

public class ValidIfDemo {

    public static void main(String[] args) {
        int age = 20;
        System.out.println("Before if statement and execute always");
        
        if(age >= 18) {
            System.out.println("Inside if statement, age is more than 18");
        }
        
        System.out.println("after if condition and execute always");
    }
}

Output:

Before if statement and execute always
Inside if statement, age is more than 18
after if condition and execute always

if we change the age value to below 18 then if block is not executed.

age = 17; // Then if condition returns false hence, statements inside if will nbe ignored.

Invalid Example:

if(age) { // Compile time error saying "Type mismatch: cannot convert from int to boolean".
    System.out.println("Inside if statement, age is more than 18");
}

Compile time error because age is integer but if statements expects boolean vlaue for evaluation.

If Else Statement:

This is useful when a condition satisfies some statements, if not satisfies then another set of statements.

If condition is true then set of specific statement else do another set of statements.

If true then
    execute a set of statements
else
    exexute another set of statements.
end if.

If Else Example:

package com.adeepdrive.statement;
public class IfElseExample {
    public static void main(String[] args) {
        int employeAge = 25;
        if (employeAge >= 21 && employeAge <= 60) {
            System.out.println("Employee age is allowed.");
        } else {
            System.out.println("Not eligible employee");
        }
    }
}

Output:

Employee age is allowed.
Because employeAge is 21. It is between 21 and 60 years.
If employeAge is 18 then output will be "Not eligible employee".

Multiple If-else statements Example:

Used when multiple conditions are present and only one will be true then its better to for multiple if-else statement.

Syntax:

if condition_expression A then
    // statements set A
else if condition_expression B then
    // statements set B
else if condition_expression C then
    // statements set C
else
    // default statements set

class MultipleIfElseDemo {
    public static void main(String[] args) {
        int testscore = 76;
        char grade;
        if (testscore >= 90) {
            grade = 'A';
        } else if (testscore >= 80) {
            grade = 'B';
        } else if (testscore >= 70) {
            grade = 'C';
        } else if (testscore >= 60) {
            grade = 'D';
        } else {
            grade = 'F';
        }
        System.out.println("Grade = " + grade);
    }
}

Output:

Grade = C

Nested If statements:

If with in If statement is said to be nested if statement. This is always legal to use.

public class NestedIfExample {
    public static void main(String[] args) {
        boolean male = true;
        boolean father = true;
        if (male) {
            if (father) {
                System.out.println("I am father");
            }
        } else {
            System.out.println("father must be male first. You are female.");
        }
    }
}

Output:

I am father