Importance of return type in Java?

A method in Java is a set of statements that can be reused in the program whenever we want. We can write a method once and call it multiple times.

• We can return values from a method; the datatype of the value we return is known as the return type. 
• We return values from a Java method using a return statement. A return statement causes the program control to transfer back to the caller of a method.
• Every method in Java is declared with a return type, and it is mandatory for all Java methods to have a return type (at least void).

A return type may be a primitive type like int, float, double, a reference type, or a void type(returns nothing). There are a few important things to keep in mind while returning values from a method -

• The type of data returned by a method must be compatible with the return type specified by the method. For instance, if the return type of some method is boolean, we can not return an integer.

• The variable receiving the value returned by a method must also be compatible with the return type specified for the method.

• The parameters can be passed in a sequence, and they must be accepted by the method in the same sequence.

Example: Returning Integer Value

The following program adds two integer values and returns their "sum" (i.e., is int type) as the result -

public class ReturnTypeTest1 {
   public int add() { // without arguments
      int x = 30;
      int y = 70;
      int z = x+y;
      return z;
   }
   public static void main(String args[]) {
      ReturnTypeTest1 test = new ReturnTypeTest1();
      int add = test.add();
      System.out.println("The sum of x and y is: " + add);
   }
}

The above program produces the following output -

The sum of x and y is: 100

Example: Returning Floating point Value

This is another example demonstrating the usage of return types in Java. We define a function with parameters that returns the product of two numbers (which is of "float" type) of those integers as the result -

public class ReturnTypeTest2 {
   public float prod(float x, float y) { // with arguments
      float z = x*y;
      return z;
   }
   public static void main(String args[]) {
      ReturnTypeTest2 test = new ReturnTypeTest2();
      float prod = test.prod(10.23f, 202.33f);
      System.out.println("The product of x and y is: " + prod);
   }
}

Following is the output of the above program -

The product of x and y is: 30

Example: Void Return Type

In the example below, we have used another return type called void. This return type is used when you don't want to return anything -

public class ReturnTypeTest2 {
   public static void display(String name){
      System.out.print("The name is: " + name);
   }
   public static void main(String[] args){
      String name = "ABC";
      display(name);
   }
}

Output

Below is the output of the above program -

The name is: ABC

Note: If the method return type is void, then do not use a return statement with a value; otherwise, you will get an error.