class Father {
public void method(){
System.out.println("This is Father's method");
}
}
class Son1 extends Father{
public void method(){
System.out.println("This is Son1's method");
}
}
class Son2 extends Father{
public void method(){
System.out.println("This is Son2's method");
}
}
public class Test {
public static void main(String[] args){
Father s1 = new Son1();
s1.method();
Father s2 = new Son2();
s2.method();
}
}
class Father {}
class Son1 extends Father{}
class Son2 extends Father{}
class Execute {
public void method(Father father){
System.out.println("This is Father's method");
}
public void method(Son1 son){
System.out.println("This is Son1's method");
}
public void method(Son2 son){
System.out.println("This is Son2's method");
}
}
public class Test {
public static void main(String[] args){
Father father = new Father();
Father s1 = new Son1();
Father s2 = new Son2();
Execute exe = new Execute();
exe.method(father);
exe.method(s1);
exe.method(s2);
}
}
運行結果如下:
This is Father's method
This is Father's method
This is Father's method
類A中的方法method1和method2的區別就是,method2是雙分派。我們可以看一下java雙分派的特點:首先要有一個訪問類B,類B提供一個showA(A a) 方法,在方法中,調用類A的method1方法,然后類A的method2方法中調用類B的showA方法并將自己作為參數傳給showA。雙分派的核心就是這個this對象。說到這里,我們已經明白雙分派是怎么回事了,但是它有什么效果呢?就是可以實現方法的動態綁定,我們可以對上面的程序進行修改,代碼如下:
class Father {
public void accept(Execute exe){
exe.method(this);
}
}
class Son1 extends Father{
public void accept(Execute exe){
exe.method(this);
}
}
class Son2 extends Father{
public void accept(Execute exe){
exe.method(this);
}
}
class Execute {
public void method(Father father){
System.out.println("This is Father's method");
}
public void method(Son1 son){
System.out.println("This is Son1's method");
}
public void method(Son2 son){
System.out.println("This is Son2's method");
}
}
public class Test {
public static void main(String[] args){
Father father = new Father();
Father s1 = new Son1();
Father s2 = new Son2();
Execute exe = new Execute();
father.accept(exe);
s1.accept(exe);
s2.accept(exe);
}
}