How to Fix Missing Return Statement Error Type in Java

1. Why Does the missing return statement Error Occur in Java
2. Fix Missing Return Statement Error Type in Java

The Java compiler might report a missing return statement error when using the if, for, or while loops in a method. This article explains why this happens and how to deal with it.

Why Does the missing return statement Error Occur in Java

One of the most common Java errors is a missing return statement.

It is an error that occurs during the compilation process. As the statement implies, the issue is usually caused by a missing return statement in the program.

Let’s take a program for reference that can produce this error.

Here is a method that returns a String type variable after determining whether or not a number passed as an argument is prime. This method utilizes the if, else, and for loops.

When we look at this program carefully, we can see the first pair of the if-else loop, each returning a String. In the else loop, we run a for loop that in turn returns a String using the if and else.

It looks alright at first glance. But after careful examination, we can find that the else statement doesn’t return anything in case the for loop fails.

In other words, the compiler doesn’t know that the for loop inside the else loop will return a String. It creates ambiguity.

Even if the for loop runs and returns a type, the compiler has to assume that there’s a possibility of it not returning anything. So to clear this confusion for the compiler, the else method should return a String type.

Java documentation suggests that if we declare a method with a return type, there needs to be a return statement at the end of the method. Otherwise, the compiler will show a missing return statement error.

This error is thrown when we mistakenly omit the return statement of the method, as it does not have a return type or has not been declared using the void type.

public class TestError {
  public static void main(String[] args) {
    System.out.println(Check_Prime(10));
    System.out.println(Check_Prime(5));
    System.out.println(Check_Prime(2));
    System.out.println(Check_Prime(1));
  }
  public static String Check_Prime(int number) {
    int i;
    if (number == 2) {
      return "Prime";
    } else {
      if (number < 2) {
        return "Not Prime";
      } else {
        for (i = 2; i <= number; i++) {
          if (number % i == 0) {
            return "Not Prime";
          } else {
            return "Prime";
          }
        }
      }
    }
  }
}

Fix Missing Return Statement Error Type in Java

public class TestError {
  public static void main(String[] args) {
    System.out.println(Check_Prime(10));
    System.out.println(Check_Prime(5));
    System.out.println(Check_Prime(2));
    System.out.println(Check_Prime(1));
  }
  public static String Check_Prime(int number) {
    int i;
    int k = number / 2;
    if (number == 2) {
      return "Prime";
    } else {
      if (number < 2) {
        return "Not Prime";
      } else {
        for (i = 2; i <= k; i++) {
          if (number % i == 0) {
            return "Not Prime";
          } else {
            return "Prime";
          }
        }
        return "";
      }
    }
  }
}

Output:

Not Prime
Prime
Prime
Not Prime