Java 重载和覆盖

我们总是说方法重载是静态多态，重写是运行时多态。这里的静态到底是什么意思？对方法的调用是否在编译代码时解析？那么普通方法调用和调用final方法有什么区别呢？编译时链接的是哪一个？

方法重载意味着根据输入创建函数的多个版本。例如：

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

调用哪个方法的选择是在编译时做出的。例如：

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

方法重写意味着通过原始方法的子类定义该方法的新版本

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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