builder简单例子

builder模式是 builder负责产生组件， 然后使用director进行组装。
实现复杂对象的构建 与 它的表示进行分离。
比如迷宫的例子。
目的 是获取一个迷宫。
迷宫的组件是 room 和 wall （并且有的wall上面需要有door）

需要的原料

public class Maze { //迷宫
    //interface 只能是 static final的成员变量  子类继承使用的时候无法改变父类的成员变量
//   Maze 包含room的集合。
//    private Room room;
    private Map roomList = new HashMap<>();// 房间号和对应的Room
    Room roomNo(int n){
        return null;
    }
    public void addRoom(String no, Room room){
        roomList.put(no, room);
    }
    public Room getRoom(String no){
        return roomList.get(no);
    }
    Maze cloneMaze(){
        return null;
    }
    public static final List mRoomList = new ArrayList<>();

    @Override
    public String toString() {
        return "Maze{" +
                "roomList=" + roomList.get("001").getSide("East") +
                '}';
    }
}

public interface DoorOrWall {
    public boolean enter();//是否可以通过
}

public class Door implements DoorOrWall{
    @Override
    public boolean enter() {
        return true;
    }
}

public class Wall implements DoorOrWall{
    //不可通过的墙壁
    @Override
    public boolean enter(){
        return false;
    }
}

然后 builder负责创建 room（添加wall） 和door（添加door）

public interface MazeBuilder {
    public T buildRoom(String room);
    public T buildDoor(String roomFrom, String roomTo);
    public Maze getMaze();
}

public class CountingMazeBuilder implements MazeBuilder{
    Maze maze = null;
    Room room = new Room();

    int _rooms;
    int _doors;
    String[] direction = {"East", "West", "South", "North"};
    public CountingMazeBuilder(){
        _rooms = _doors = 0;
    }

    @Override
    public CountingMazeBuilder buildRoom(String roomNum) {
        room.setSide(direction[3], new Wall());

        maze.addRoom(roomNum, room);
        return this;
    }

    @Override
    public CountingMazeBuilder buildDoor(String roomFrom, String roomTo) {

        Room room1 = maze.getRoom(roomFrom);
        Room room2 = maze.getRoom(roomTo);
        Door door = new Door();
        if(room1 != null){
            System.out.println("room1 not null");
        }
        if(room1 == null){
            System.out.println("room1 null");
        }
        room1.setSide("East", door);
        return this;
    }

    @Override
    public Maze getMaze() {
        return maze;
    }

    //CountingMazeBuilder 自己的3个方法 而上面的是继承Builder的方法。
    public CountingMazeBuilder buildMaze(){
        //实例化 maze
        this.maze = new Maze();
        return this;
    }
    void addWall(int x, String[] direction){

    }
    void getCounts(int x, int y){}
}

director 导向或者组装器

public class Director {
    private CountingMazeBuilder builder;
    public Director(CountingMazeBuilder builder){
        this.builder = builder;
    }
    public void construct(){
        builder.buildMaze()
        .buildRoom("001") //
        .buildDoor("001", "002");
    }
}

测试

public class MazeDriver {
    public static void main(String[] args) {
        CountingMazeBuilder builder = new CountingMazeBuilder();
        Director director = new Director(builder);
        director.construct();//给上面的builder  赋值（先实例化Maze，然后添加room）
        Maze maze = builder.getMaze();
        System.out.println(maze);
    }
}

Director中一直持有 builder 在执行construct方法（给builder中字段Maze添加room） 进入Builder中 set值， 然后builder中字段Maze.addRoom() 然后就可以getMaze()获取迷宫了

结果