访问者模式 (Visitor Pattern)

1、类图

2、代码

public class Main {

    public static void main(String[] args) {
        ComputerPart computer = new Computer();
        computer.accept(new ComputerPartDisplayVisitor());
    }
}

// 您在朋友家做客，您是访问者，朋友接受您的访问，您通过朋友的描述，然后对朋友的描述做出一个判断
interface ComputerPartVisitor {
    public void visit(Computer computer);
    public void visit(Mouse mouse);
    public void visit(Keyboard keyboard);
    public void visit(Monitor monitor);
}

class ComputerPartDisplayVisitor implements ComputerPartVisitor {
    
    @Override
    public void visit(Computer computer) {
        System.out.println("Displaying Computer.");
    }
    @Override
    public void visit(Mouse mouse) {
        System.out.println("Displaying Mouse.");
    }
    @Override
    public void visit(Keyboard keyboard) {
        System.out.println("Displaying Keyboard.");
    }
    @Override
    public void visit(Monitor monitor) {
        System.out.println("Displaying Monitor.");
    }
}

// 接受访问
interface ComputerPart {
    public void accept(ComputerPartVisitor computerPartVisitor);
}

class Keyboard implements ComputerPart {
    
    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        computerPartVisitor.visit(this);
    }
}
class Monitor implements ComputerPart {
    
    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        computerPartVisitor.visit(this);
    }
}
class Mouse implements ComputerPart {
    
    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        computerPartVisitor.visit(this);
    }
}

class Computer implements ComputerPart {
    
    ComputerPart[] parts;

    public Computer(){
        parts = new ComputerPart[] {new Mouse(), new Keyboard(), new Monitor()};      
    }
    
    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        for(int i = 0; i < parts.length; i++) {
            parts[i].accept(computerPartVisitor);
        }
        computerPartVisitor.visit(this);
    }
}