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
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
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

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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.
**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.
**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.

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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
**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
**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

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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");
            }
        }
    }
}
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");
            }
        }
    }
}
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");
            }
        }
    }
}

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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
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
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

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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
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
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

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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
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
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

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python

a = 2.2
      b = 5.4
if b > a:
    print("B is greater than a")
output:
  num is greater than or equal 120
a = 2.2
      b = 5.4
if b > a:
    print("B is greater than a")

output:
  num is greater than or equal 120
a = 2.2
      b = 5.4
if b > a:
    print("B is greater than a")

output:
  num is greater than or equal 120

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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
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
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

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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
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
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

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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

原文链接：if else and nested if in java: