if else and nested if in java:

If statement:
if a certain condition is true then a block of statements is executed otherwise not.

Syntax:

If (condition){
//code to be executed
}

program:
public class If {  
public static void main(String[] args) {  
      float a =2.2f; 
      float b =5.4f; 
        if(b>a)
         {  
          System.out.println(" B is greater than a");  
           }  
       }  
}  


Output:
B is greater than a

if-else statement: 
In Java, the if-else condition is a set of rules or statements,It executes one block of code if a condition is true and another block if the condition is false.

Syntax:

If(condition){
// code if condition is true
}else{
//code if condition is false
}

**program**:

public class IfElse {

    public static void main(String[] args) {

        int n = 3;

        if (n > 5) {
            System.out.println("The number is greater than 5.");
        } 
         else  
        {
            System.out.println("The number is 5 or less.");
        }
    }
}


Output:
The number is 5 or less.

The else if Statement:

Use the else if statement to specify a new condition if the first condition is false.

Syntax:
if (condition1) {
// block of code to be executed if condition1 is true
} else if (condition2) {
// block of code to be executed if the condition1 is false and condition2 is true
} else {
// block of code to be executed if the condition1 is false and condition2 is false
}

**program:**

public class Greater
{
public static void main (String args[])
{
int no1 = 1000; 
        int no2 = 1000; 
        if(no1>no2)
          {
            System.out.println("no1 is greater");
          }
        else if(no2>no1)
         {
              System.out.println("no2 is greater");
         }      
        else 
           {
         System.out.println("Both are equal");
           }
}
}

output:
     Both are equal

Nested if in Java
Refers to having one if statement inside another if statement. If the outer condition is true the inner conditions are checked and executed accordingly.

*Syntax of Nested if *

if (condition1) {
if (condition2) {
if (condition3) {
// statements;
}
}
}

program:

    public class nested if
    {
    public static void main(String args[])
    {
        int a = 10;
        int b = 20;

        // Outer if condition
        if (a == 10) {

            // Inner if condition
            if (b != 20) {
                System.out.println("GeeksforGeeks");
            }

            else {
                System.out.println("GFG");
            }
        }
    }
}

Task: program:1

java

public class Age
{
public static void main (String args[])
{
 int age1=25;
 int age2=21;
    if(age1<age2)
{
       System.out.println("The condition is false");
}
    else 
{
       System.out.println("The condition is true");
}
}
}

output:
 The condition is true

python

age1 = 25
age2 = 21

if age1 < age2:
    print("The condition is false")
elif age2 < age1:
    print("The condition is true")

output:
The condition is true

java

program:2

public class If {  
public static void main(String[] args) {  
      float a =2.2f; 
      float b =5.4f; 
        if(b>a)
         {  
          System.out.println(" B is greater than a");  
           }  
       }  
}  

output:
B is greater than a

python

a = 2.2
      b = 5.4
if b > a:
    print("B is greater than a")

output:
  num is greater than or equal 120

java

program:3

public class Greater
{
public static void main (String args[])
{
int no1 = 1000; 
        int no2 = 1000; 
        if(no1>no2)
          {
        System.out.println("no1 is greater");
          }
        else if(no2>no1)
         {
           System.out.println("no2 is greater");
         }      
        else 
           {
      System.out.println("Both are equal");
           }
}
}

output:
Both are equal

python

no1 = 1000
no2 = 1000

if no1 > no2:
    print("no1 is greater")
elif no2 > no1:
    print("no2 is greater")
else:
    print("Both are equal")

output:
Both are equal

References:https://www.javatpoint.com/java-if-else
References:https://www.geeksforgeeks.org/java-if-else-statement-with-examples/
References:https://www.w3schools.com/java/java_conditions.asp