Java重载和覆盖 [英] Java overloading and overriding

问题描述

我们总是说方法重载是静态多态，而重写是运行时多态。静态到底是什么意思？在编译代码时是否解析了对方法的调用？那么普通方法调用和调用最终方法之间的区别是什么呢？哪一个在编译时链接？

We always say that method overloading is static polymorphism and overriding is runtime polymorphism. What exactly do we mean by static here? Is the call to a method resolved on compiling the code? So whats the difference between normal method call and calling a final method? Which one is linked at compile time?

推荐答案

方法重载意味着根据输入创建函数的多个版本。例如：

Method overloading means making multiple versions of a function based on the inputs. For example:

public Double doSomething(Double x) { ... }
public Object doSomething(Object y) { ... }

选择要在编译时调用的方法。例如：

The choice of which method to call is made at compile time. For example:

Double obj1 = new Double();
doSomething(obj1); // calls the Double version

Object obj2 = new Object();
doSomething(obj2); // calls the Object version

Object obj3 = new Double();
doSomething(obj3); // calls the Object version because the compilers see the 
                   // type as Object
                   // This makes more sense when you consider something like

public void myMethod(Object o) {
  doSomething(o);
}
myMethod(new Double(5));
// inside the call to myMethod, it sees only that it has an Object
// it can't tell that it's a Double at compile time

方法覆盖是指通过原始子类定义新方法的方法

Method Overriding means defining a new version of the method by a subclass of the original

class Parent {
  public void myMethod() { ... }
}
class Child extends Parent {
  @Override
  public void myMethod() { ... }
}

Parent p = new Parent();
p.myMethod(); // calls Parent's myMethod

Child c = new Child();
c.myMethod(); // calls Child's myMethod

Parent pc = new Child();
pc.myMethod(); // call's Child's myMethod because the type is checked at runtime
               // rather than compile time

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