How to solve Java method return value exception (IllegalReturnValueException)-javaTutorial-php.cn

How to solve Java method return value exception (IllegalReturnValueException)

In Java programming, we often encounter method return value exception (IllegalReturnValueException). This exception is usually caused by the method return value not matching the method declaration or returning an illegal value. This article will introduce the causes and solutions of common IllegalReturnValueException, and provide some code examples.

Cause Analysis
IllegalReturnValueException usually occurs in the following situations:
The method return type is inconsistent with the method declaration: the method declares the return type to be a certain class or interface, but the actual Other types are returned.
The return value does not comply with the constraints in the method declaration: for example, the method declares that the return value cannot be null, but actually returns null.
Return value type mismatch: The method declares the return type to be a collection type, but actually returns other types.
Internal logic error in the method: The logic error inside the method leads to an illegal return value.
Solution
2.1 Check whether the method declaration and return type are consistent
First, check whether the method declaration and return type are consistent. Make sure that the method's declared return type matches the actual return type. If the return type declared by the method is an interface or abstract class, then the actual return type should be the concrete implementation class of the interface or abstract class.

Sample code:

public interface Animal { String getName(); } public class Cat implements Animal { @Override public String getName() { return "Cat"; } public static void main(String[] args) { Animal animal = new Cat(); System.out.println(animal.getName()); // 输出 "Cat" } }

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2.2 Check whether the return value satisfies the constraints
If the method declares that the return value is not allowed to be null or should satisfy other constraints, then it should be in Check inside the method. If the return value does not meet the constraints, you can actively throw exceptions such as IllegalArgumentException, or return a specific default value.

Sample code:

public String getNotNullValue() { String value = generateValue(); if (value == null) { throw new IllegalArgumentException("Value should not be null"); } return value; }

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2.3 Ensure that the return value type is consistent with the declaration
If the method declares a return value of a certain type, then you must ensure that the actual returned value is compatible. For example, if a method declares that it returns an object of type List, the actual returned value must be a List object.

Sample code: