类的功能层次结构和实现层次结构的分离

1 - 负责”显示”的类

public class Display {
    private DisplayImpl impl;
    public Display(DisplayImpl impl){
        this.impl = impl;
    }

    public void open(){
        impl.rawOpen();
    }

    public void print(){
        impl.rawPrint();
    }

    public void close(){
        impl.rawClose();
    }

    public final void display(){
        open();
        print();
        close();
    }
}

2 - 增加了”只显示规定次数”这一功能的类

public class CountDisplay extends Display{
    public CountDisplay(DisplayImpl impl) {
        super(impl);
    }

    public void multiDisplay(int times){
        open();
        for (int i = 0; i < times; i++) {
            print();
        }
        close();
    }
}

3 - 负责”显示”的类

public abstract class DisplayImpl {
    public abstract void rawOpen();
    public abstract void rawPrint();
    public abstract void rawClose();
}

4 - “用字符串显示”的类

public class StringDisplayImpl extends DisplayImpl{
    private String string;
    private int width;

    public StringDisplayImpl(String string){
        this.string = string;
        this.width = string.getBytes().length;
    }
    @Override
    public void rawOpen() {
        printLine();
    }

    @Override
    public void rawPrint() {
        System.out.println("|" + string + "|");
    }

    @Override
    public void rawClose() {
        printLine();
    }

    private void printLine(){
        System.out.print("+");
        for (int i = 0; i < width; i++) {
            System.out.print("-");
        }
        System.out.println("+");
    }
}

5 - 测试程序的类

public class Main {
    public static void main(String[] args) {
        Display d1 = new Display(new StringDisplayImpl("Hello, China."));
        Display d2 = new CountDisplay(new StringDisplayImpl("Hello, World."));
        CountDisplay d3 = new CountDisplay(new StringDisplayImpl("Hello, Universe."));

        d1.display();
        d2.display();
        d3.display();
        d3.multiDisplay(3);
    }
}

6 - 输出示例

+-------------+
|Hello, China.|
+-------------+
+-------------+
|Hello, World.|
+-------------+
+----------------+
|Hello, Universe.|
+----------------+
+----------------+
|Hello, Universe.|
|Hello, Universe.|
|Hello, Universe.|
+----------------+