Hello LUYEE

Builder模式用大白话讲就是：我有一个东西构造起来很复杂，那我就定义一个工厂类，专门负责构建这个复杂对象。

比如下面的例子，Builder<T>泛型接口很简单，只定义了一个能返回泛型类型参数T型的对象引用。

interface Builder<T> {
    public T build();
}

然后下面的代码，在不可变的ImmutableClass类的内部套嵌着一个可变的配套工厂类ImmuBuilder。

final class ImmutableClass {
    private final int a;
    private final int b;
    private final int c;
    private final int d;
    private final int e;
    private ImmutableClass(ImmuBuilder b){
        a = b.a;
        b = b.b;
        c = b.c;
        d = b.d;
        e = b.e;
    }
    static final class ImmuBuilder implements Builder<ImmutableClass> {
        private final int a;
        private final int b;
        private final int c;
        private final int d;
        private final int e;
        public int setA(int num) { a = num; }
        public int setB(int num) { b = num; }
        public int setC(int num) { c = num; }
        public int setD(int num) { d = num; }
        public int setE(int num) { e = num; }
        public ImmutableClass build() {
            return new ImmutableClass(this);
        }
    }
}

Builder Pattern

| java design pattern builder pattern |

Builder模式