[开发工具]stream流操作

stream流基本操作

public class TestStream {
    public static void main(String[] args) {
        List<House> houseList = new ArrayList<>();
        houseList.add(House.HouseBuilder.create().setColumn("钢柱").setBeam(null).setFloor("钢地板").setWall("玻璃墙").build());
        houseList.add(House.HouseBuilder.create().setColumn("木柱").setBeam("钢梁").setFloor("木地板").setWall("木墙").build());
        houseList.add(House.HouseBuilder.create().setColumn("木柱").setBeam("木梁").setFloor(null).setWall("白灰墙").setStairs("螺旋楼梯").build());
        houseList.add(House.HouseBuilder.create().setColumn(null).setBeam("钢梁").setFloor("瓷砖").setWall("瓷砖墙").setStairs("旋转楼梯").build());
        houseList.add(House.HouseBuilder.create().setColumn(null).setBeam("钢筋").setFloor("大理石").setWall(null).build());
        houseList.add(House.HouseBuilder.create().setColumn("钢筋").setBeam(null).setFloor("水磨石").setWall("清水砖墙").build());

        System.out.println("=============list转string,list,set,map===============");
        String collect = houseList.stream().filter(r -> Objects.nonNull(r.getWall())).filter(r -> !r.getWall().startsWith("瓷")).map(House::getWall).collect(Collectors.joining(","));
        List<String> beamList = houseList.stream().map(House::getBeam).collect(Collectors.toList());
        Set<String> wallSet = houseList.stream().filter(r -> Objects.nonNull(r.getFloor())).map(House::getWall).collect(Collectors.toSet());
        Map<String, String> wallAndFloorMap = houseList.stream().filter(r -> Objects.nonNull(r.getFloor())).collect(Collectors.toMap(House::getWall, House::getFloor));
        System.out.println("=============list转string===============");
        System.out.println(collect);
        System.out.println("=============list转list===============");
        beamList.forEach(r -> System.out.println(r));
        System.out.println("=============list转set===============");
        wallSet.forEach(r -> System.out.println(r));
        System.out.println("=============list转map===============");
        wallAndFloorMap.forEach((k, v) -> System.out.println(k + "============" + v));

        System.out.println("=============map转list,map===============");
        System.out.println("=============map转list===============");
        List<String> map2List = wallAndFloorMap.entrySet().stream().filter(r -> r.getValue().endsWith("石")).map(r -> r.getValue().concat("地板")).collect(Collectors.toList());
        map2List.forEach(r -> System.out.println(r));
        System.out.println("=============map转map===============");
        Map<String, String> map2Map = wallAndFloorMap.entrySet().stream().filter(r -> Objects.nonNull(r.getKey())).filter(r -> r.getValue().length() > 2).collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
        map2Map.forEach((k, v) -> System.out.println(k + "========" + v));
    }
}

class House {
    private String wall;
    private String floor;
    private String column;
    private String beam;
    private String stairs;

    public String getWall() {
        return wall;
    }

    public String getFloor() {
        return floor;
    }

    public String getColumn() {
        return column;
    }

    public String getBeam() {
        return beam;
    }

    public String getStairs() {
        return stairs;
    }

    private House(HouseBuilder builder) {
        this.wall = builder.wall;
        this.floor = builder.floor;
        this.column = builder.column;
        this.beam = builder.beam;
        this.stairs = builder.stairs;
    }

    static class HouseBuilder {
        private String wall;
        private String floor;
        private String column;
        private String beam;
        private String stairs;

        public static HouseBuilder create() {
            return new HouseBuilder();
        }

        public House build() {
            return new House(this);
        }

        public HouseBuilder setFloor(String floor) {
            this.floor = floor;
            return this;
        }

        public HouseBuilder setColumn(String column) {
            this.column = column;
            return this;
        }

        public HouseBuilder setWall(String wall) {
            this.wall = wall;
            return this;
        }

        public HouseBuilder setBeam(String beam) {
            this.beam = beam;
            return this;
        }

        public HouseBuilder setStairs(String stairs) {
            this.stairs = stairs;
            return this;
        }

        @Override
        public String toString() {
            return "HouseBuilder{" +
                    "wall='" + wall + '\'' +
                    ", floor='" + floor + '\'' +
                    ", column='" + column + '\'' +
                    ", beam='" + beam + '\'' +
                    ", stairs='" + stairs + '\'' +
                    '}';
        }
    }
}

建造者模式

使用场景：参数比较多，一般多于4个，有必填也有非必填。
1.在House中创建一个静态内部类 HouseBuilder，然后将House中的参数都复制到HouseBuilder类中。
2.在House中创建一个private的构造函数，参数为HouseBuilder类型
3.在HouseBuilder中创建设置函数，对House中那些可选参数进行赋值，返回值为HouseBuilder类型的实例
4.在HouseBuilder中创建一个build()方法，在其中构建House的实例并返回