当方法定义为 int 数据类型时，如何在 Java 中返回 null？

Question

I've been doing a code where its mandatory to use the data type cannot be void and I don't need to return anything.

Answer 1

In Java, null is only a valid value for reference types. It cannot represent a primitive type such as int . Here are some alternatives to consider:

1. If you are using Java 8 or later, and are able to change the return type of the method you could use the OptionalInt type to represent an int value that may or may not be present. In that case, you would return OptionalInt.empty() in the case that there is no int value to return, and OptionalInt.of(x) to return an int x . Note that the caller will need to unwrap the int value (if it is present) using one of the other methods available on that class. This approach is often preferred for new code, as it makes the intention and usage very clear.
2. If you are using an older Java version, another possibility is to change the return type to Integer . This is a wrapper class for int values that does allow for null to be returned. In addition, Java's auto-unboxing rules allow it to be used in contexts where an int value is expected, when the value is not null . However, if a null value is unboxed to an int value, it will result in a NullPointerException , so it is important to check for null before performing operations that would result in unboxing.
3. If you need to use the int return type, it is common to use a sentinal value to represent an abnormal return. For example, if the normal return values for the method are all non-negative integers, you could use a value such as -1 to represent an absent return value. This is commonly used in older JDK methods such as String.indexOf() .
4. In some cases, it makes sense to throw an Exception when no valid value can be returned. It's only a good idea to use this approach for truly exceptional circumstances, as the runtime cost for throwing exceptions is much higher than normal method returns, and the flow of control can make the code harder to understand.