Why does a subclass report an error when calling an overloaded method?

In Java, it is very common for subclasses to report errors when calling overloaded methods. Overloading refers to the situation where multiple methods with the same name are defined in a class but with different parameter lists. If a subclass wants to call an overloaded method in the parent class, compilation errors sometimes occur. Next, I will use specific code examples to illustrate the reasons why subclasses report errors when calling overloaded methods.

Suppose we have a parent class ParentClass, which defines two overloaded methods:

public class ParentClass {
    public void printInfo(String str) {
        System.out.println("Printing String: " + str);
    }

    public void printInfo(int num) {
        System.out.println("Printing Integer: " + num);
    }
}

Next, we create a subclass ChildClass and try to call the overloaded method in the parent class:

public class ChildClass extends ParentClass {
    public void printInfo(double val) {
        System.out.println("Printing Double: " + val);
    }

    public static void main(String[] args) {
        ChildClass child = new ChildClass();
        child.printInfo("Hello"); // 这行代码会报错
    }
}

In the above code, the subclass ChildClass inherits the parent class ParentClass and defines a new overloaded method printInfo(double val). In the main method, we create an instance child of ChildClass and try to call the printInfo(String str) method in the parent class.

However, when we try to compile the above code, we will receive the following compilation error:

Error: method printInfo in class ParentClass cannot be applied to given types;
required: int
found: java.lang.String

The reason for this error is that when Java calls a method, it is based on the number and type of parameters passed in. to determine the specific method to call. In this case, the subclass ChildClass tries to call the printInfo(String str) method in the parent class, but since this method is not overloaded in the subclass, the compiler will look for the best matching method and find that only the printInfo(int num) method The call can be completed, but printInfo(String str) cannot be found.

In order to solve this problem, we can override the overloaded method in the parent class in the subclass, or explicitly call the overloaded method in the parent class. For example:

public class ChildClass extends ParentClass {
    @Override
    public void printInfo(String str) {
        System.out.println("Overriding method in ChildClass: " + str);
    }

    public void callParentMethod(String str) {
        super.printInfo(str); // 显式调用父类中被重载的方法
    }

    public static void main(String[] args) {
        ChildClass child = new ChildClass();
        child.printInfo("Hello"); // 调用子类中重写的方法
        child.callParentMethod("World"); // 显式调用父类中的重载方法
    }
}

By overriding methods in the parent class or explicitly calling parent class methods, we can avoid errors when subclasses call overloaded methods. In this way, you can better understand the reasons why subclasses report errors when calling overloaded methods, and learn how to solve such problems.

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