通过Builder来构建集合list和map

之前已经写过一篇通用Builder来构建实例对象的（基于Java8的新特性写一个通用的Builder工具类_java手动写一个builder-CSDN博客）但是这个builder不能构建集合，也就是list和map，今天突然心血来潮，想写写集合类的builder，这两个builder相比于通用的builder要简单易懂的多，废话不多说，直接上代码：

Mapbuilder：

public class MapBuilder<K, V> {
    private Map<K, V> map;

    private MapBuilder(Map<K, V> map) {
        this.map = map;
    }

    public static <K, V> MapBuilder<K, V> ofMap() {
        return new MapBuilder<>(new HashMap<K, V>());
    }

    public MapBuilder<K, V> put(K key, V value) {
        this.map.put(key, value);
        return this;
    }

    public Map<K, V> build() {
        return this.map;
    }

    public static void main(String[] args) {
        Map<String, Integer> map = MapBuilder.<String, Integer>ofMap()
                .put("a", 1)
                .put("b", 2)
                .put("c", 3)
                .build();

        System.out.println(map); // 输出：{a=1, b=2, c=3}
    }
}

ListBuilder:

public class ListBuilder<T> {
    private List<T> list;

    private ListBuilder(List<T> list) {
        this.list = list;
    }

    public static <T> ListBuilder<T> ofList() {
        return new ListBuilder(new ArrayList<T>());
    }

    public ListBuilder<T> add(T t) {
        this.list.add(t);
        return this;
    }

    public List<T> build() {
        return this.list;
    }

    public static void main(String[] args) {
        List<Integer> integers = ListBuilder.<Integer>ofList().add(1).build();
        System.err.println(integers);
    }
}