If you are interested to learn about the Java math

Java Conditions and If Statements

if statement is used to test the condition. It checks boolean condition: true or false. There are various types of if statement in Java. Java supports the usual logical conditions from mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions. Java has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

The if Statement

Use the if statement to specify a block of Java code to be executed if a condition is true.

Syntax

if (condition) {
  // block of code to be executed if the condition is true
}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error. In the example below, we test two values to find out if 20 is greater than 18. If the condition is true, print some text:

Example

if (20 > 18) {
  System.out.println("20 is greater than 18");
}

We can also test variables:

Example

int x = 20;
int y = 18;
if (x > y) {
  System.out.println("x is greater than y");
}

Example explained

In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that “x is greater than y”.

The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax

if (condition) {
  // block of code to be executed if the condition is true
} else {
  // block of code to be executed if the condition is false
}

Example

int time = 20;
if (time < 18) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}
// Outputs "Good evening.

Example explained

In the example above, time (20) is greater than 18, so the condition is false. Because of this, we move on to the else condition and print to the screen “Good evening”. If the time was less than 18, the program would print “Good day”.

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
}

Example

int time = 22;
if (time < 10) {
  System.out.println("Good morning.");
} else if (time < 20) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}
// Outputs "Good evening."

Java if-else-if ladder Statement

The if-else-if ladder statement executes one condition from multiple statements.

Syntax:

if(condition1){  
//code to be executed if condition1 is true  
}else if(condition2){  
//code to be executed if condition2 is true  
}  
else if(condition3){  
//code to be executed if condition3 is true  
}  
...  
else{  
//code to be executed if all the conditions are false  
}  

Example:

//Java Program to demonstrate the use of If else-if ladder.  
//It is a program of grading system for fail, D grade, C grade, B grade, A grade and A+.  
public class IfElseIfExample {  
public static void main(String[] args) {  
    int marks=65;  
      
    if(marks<50){  
        System.out.println("fail");  
    }  
    else if(marks>=50 && marks<60){  
        System.out.println("D grade");  
    }  
    else if(marks>=60 && marks<70){  
        System.out.println("C grade");  
    }  
    else if(marks>=70 && marks<80){  
        System.out.println("B grade");  
    }  
    else if(marks>=80 && marks<90){  
        System.out.println("A grade");  
    }else if(marks>=90 && marks<100){  
        System.out.println("A+ grade");  
    }else{  
        System.out.println("Invalid!");  
    }  
}  
}  

Output:

C grade

Program to check POSITIVE, NEGATIVE or ZERO:

public class PositiveNegativeExample {    
public static void main(String[] args) {    
    int number=-13;    
    if(number>0){  
    System.out.println("POSITIVE");  
    }else if(number<0){  
    System.out.println("NEGATIVE");  
    }else{  
    System.out.println("ZERO");  
   }  
}    
}    

Output:

NEGATIVE

Java Nested if statement

The nested if statement represents the if block within another if block. Here, the inner if block condition executes only when outer if block condition is true.

Syntax:

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

Example:

//Java Program to demonstrate the use of Nested If Statement.  
public class JavaNestedIfExample {    
public static void main(String[] args) {    
    //Creating two variables for age and weight  
    int age=20;  
    int weight=80;    
    //applying condition on age and weight  
    if(age>=18){    
        if(weight>50){  
            System.out.println("You are eligible to donate blood");  
        }    
    }    
}}  

Output:

You are eligible to donate blood

Example 2:

//Java Program to demonstrate the use of Nested If Statement.    
public class JavaNestedIfExample2 {      
public static void main(String[] args) {      
    //Creating two variables for age and weight    
    int age=25;    
    int weight=48;      
    //applying condition on age and weight    
    if(age>=18){      
        if(weight>50){    
            System.out.println("You are eligible to donate blood");    
        } else{  
            System.out.println("You are not eligible to donate blood");    
        }  
    } else{  
      System.out.println("Age must be greater than 18");  
    }  
}  }  

Output:

You are not eligible to donate blood

Java Short Hand If…Else (Ternary Operator)

Short Hand If…Else

There is also a short-hand if else, which is known as the ternary operator because it consists of three operands. It can be used to replace multiple lines of code with a single line, and is most often used to replace simple if else statements:

Syntax

variable = (condition) ? expressionTrue :  expressionFalse;

Instead of writing:

Example

int time = 20;
if (time < 18) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}

You can simply write:

Example

int time = 20;
String result = (time < 18) ? "Good day." : "Good evening.";
System.out.println(result);