[20210628] 静态类

静态类只能作为内部类出现，一般用于Builder模式。

public class Outer {
    private String name;
    private int age;
    public static class Builder {
        private String name;
        private int age;
        public Builder(int age) {
            this.age = age;
        }
        public Builder withName(String name) {
            this.name = name;
            return this;
        }
        public Builder withAge(int age) {
            this.age = age;
            return this;
        }
        public Outer build() {
            return new Outer(this);
        }
    }
    private Outer(Builder b) {
        this.age = b.age;
        this.name = b.name;
    }
}

、
优点在于，调用的时候不需要实例化外部。

public Outer getOuter()
{
    Outer outer = new Outer.Builder(2).withName("xx").build();
    return outer;
}