# If-Else : 1
### What is the usecase of if-else?

> **If else** is used in case of **boolean conditions** where we want to execute a piece of code if a condition is true or false.

> The condition should be boolean i.e output of the condition should be either **true** or **false**.

> For example: Let's say We are making a system for senior citizens wherein a person can get pension if that person is 65 or older otherwise he/she can't. Here the condition is age of the person.

Condition :

if (age >= 65);

# If block :
> **When we only want to do something when condition is true**

Code1 :

int a = 9;
if( a >= 10 ){
    System.out.println("inside if block");
}
System.out.println("outside if block");

Output :

outside if block

Explanation :

Condition: a >= 10 gives false therefore code inside if block does not gets executed.

Code2 :
- Using multiple if conditions

int a=18,b=16;
if ( a >= 18 ) { 
    System.out.println("a is major");
}
if ( b >= 18 ) { 
    System.out.println("b is major");
}
System.out.println("Blab");

Output :

a is major
Blab

Explanation :

Condition: a >= 18 is true hence first if block code is executed
Condition: b >= 18 is false hence code inside second if block is not executed.

Code3 :
- Using multiple if conditions

int a = 50, b=50;
if ( a >= 50 ) {
    System.out.println("a scored half");
    a = a+1;
}
if ( b >= 50 ) {
    System.out.println("b scored half");
    b = b+1;
}
System.out.print(a+b);

Output :

a scored half
b scored half
102

Explanation :

-> Condition: a >= 50 is true hence first if block code is executed. Value of a incremented by factor of 1.
-> Condition: b >= 50 is true hence second if block code is also executed. Value of b incremented by factor of 1.
-> Total = 51 + 51 = 102

# If - else block :

> In case if we want to do some work when condition is true we use only if block, but when we want to do work when condition is false → Use If - Else

> When condition is true if block is executed. When condition is false else block is executed.

Code1 :

if ( 9 > 5 ){
    System.out.println("If block");
} else {
    System.out.println("Else block");
} 
System.out.println(("Outside if else"));
    

Output :

If block
Outside if else

Explanation :

-> Condition: 9 > 5 gives true therefore code inside if block gets executed.
-> Then code outside if else block gets executed 

Code2 :

 if ( false ) {
     System.out.println("if block");
} else {
     System.out.println("else block");
}

Output :

else block

Explanation :

Condition is false therefore code inside else block gets executed.

### If else-if block:
> This block is used when we have multiple conditions to check.

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
}

Explanation :

-> If block : Will be executed if condition1 is true
-> else if block : Will be executed if the condition1 is false and condition2 is true
-> else block : Will be executed if both Condition1 and Condition2 are false.

Code :

int time = 22;
if (time < 10) {
  System.out.println("Good morning.");
} else if (time == 22) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}
System.out.println("Outside all blocks");

Output :

Good day.
Outside all blocks

Explanation

-> Since our condition i.e time == 22 is true hence else if block is executed.
-> Last print statement will be executed by default as it is outside if-else blocks

### Note:
- Always use brackets in pairs.
- Be careful when writing conditions inside if-else blocks.
- Keep in mind that java is case sensitive while writing if and else words.