子类重写和隐藏父类的成员方法(Overriding and Hiding Methods)

先看一个例子：

public class Animal {public static void testClassMethod() {System.out.println("The static method in Animal");}public void testInstanceMethod() {System.out.println("The instance method in Animal");}}

</pre><pre name="code" class="html">public class Cat extends Animal {public static void testClassMethod() {System.out.println("The static method in Cat");}public void testInstanceMethod() {System.out.println("The instance method in Cat");}public static void main(String[] args) {Cat myCat = new Cat();Animal myAnimal = myCat;Animal.testClassMethod();myAnimal.testInstanceMethod();}}

the output:The static method in AnimalThe instance method in CatHere, The 

Cat

 classoverrides the instance method in 

Animal

 and hidesthe static method in 

Animal

. The 

main

 methodin this class creates an instance of 

Cat

 and invokes

testClassMethod()

 onthe class and 

testInstanceMethod()

 on the instance.Summary:

Instance Methods

An instance method in a subclass with the same signature (name, plus the number and the type of its parameters) and return type as an instance method in the superclassoverrides thesuperclass's method.The ability of a subclass to override a method allows a class to inherit from a superclass whose behavior is "close enough" and then to modify behavior as needed. The overriding methodhas the same name, number and type of parameters, and return type as the method that it overrides. An overriding method can also return a subtype of the type returned by the overridden method. This subtype is called a covariant return type.

Static Methods

If a subclass defines a static method with the same signature as a static method in the superclass, then the method in the subclass hides the one in the superclass.The distinction between hiding a static method and overriding an instance method has important implications:The version of the overridden instance method that gets invoked is the one in the subclass.The version of the hidden static method that gets invoked depends on whether it is invoked from the superclass or the subclass.