Builder建造者设计模式

目录

案例一 

案例二

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使用场景：当构建一个复杂的对象需要传入很多参数的时候，或者是一个对象的属性有很多，但是使用时也许只需要这个对象的几个属性，如果使用构造器的话，就得将不需要的参数也传个null进去，比方说一个对象有100个属性，但是我只需要里面的2个属性，那我得new对象时传98个null进去，这两种情况下就可以选择使用建造者模式。 

案例一 

实体类 

public class Terrain {
    Wall w;
    Fort f;
    Mine m;
}

class Wall {
    int x, y, w, h;

    public Wall(int x, int y, int w, int h) {
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
    }
}

class Fort {
    int x, y, w, h;

    public Fort(int x, int y, int w, int h) {
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
    }

}

class Mine {
    int x, y, w, h;

    public Mine(int x, int y, int w, int h) {
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
    }
}

 接口

每个方法的返回值都是TerrainBuilder对象，就可以实现链式编程。

public interface TerrainBuilder {
    TerrainBuilder buildWall();
    TerrainBuilder buildFort();
    TerrainBuilder buildMine();
    Terrain build();
}

实现 

public class ComplexTerrainBuilder implements TerrainBuilder {
    Terrain terrain = new Terrain();

    @Override
    public TerrainBuilder buildWall() {
        terrain.w = new Wall(10, 10, 50, 50);
        return this;
    }

    @Override
    public TerrainBuilder buildFort() {
        terrain.f = new Fort(10, 10, 50, 50);
        return this;
    }

    @Override
    public TerrainBuilder buildMine() {
        terrain.m = new Mine(10, 10, 50, 50);
        return this;
    }

    @Override
    public Terrain build() {
        return terrain;
    }
}

测试 

public class Main {
    public static void main(String[] args) {
        TerrainBuilder builder = new ComplexTerrainBuilder();
        Terrain t = builder.buildFort().buildMine().buildWall().build();
    }
}

案例二

Person类，假设有100个参数 

public class Person {
    int id;
    String name;
    int age;
    double weight;
    int score;
    Location loc;

    private Person() {}

    public static class PersonBuilder {
        Person p = new Person();

        public PersonBuilder basicInfo(int id, String name, int age) {
            p.id = id;
            p.name = name;
            p.age = age;
            return this;
        }

        public PersonBuilder weight(double weight) {
            p.weight = weight;
            return this;
        }

        public PersonBuilder score(int score) {
            p.score = score;
            return this;
        }

        public PersonBuilder loc(String street, String roomNo) {
            p.loc = new Location(street, roomNo);
            return this;
        }

        public Person build() {
            return p;
        }
    }
}

class Location {
    String street;
    String roomNo;

    public Location(String street, String roomNo) {
        this.street = street;
        this.roomNo = roomNo;
    }
}

测试

public class Main {
    public static void main(String[] args) {
        Person p = new Person.PersonBuilder()
                .basicInfo(1, "zhangsan", 18)
                //.score(20)
                .weight(200)
                //.loc("bj", "23")
                .build();
    }
}