小编Gus*_*ust的帖子

我有以下课程:

public abstract class A {

    public String att;

    public static abstract class Builder<T extends A> {

        public T a;

        public abstract T build();

        public T.Builder setAtt(String a) {
            this.a.att = a;
            return this;
        }
    }
}

public class A1 extends A {

    public static class Builder extends A.Builder<A1> {

        public Builder() {
            this.a = new A1();
        }

        public A1 build() {
            return this.a;
        }
    }
} 

public class A2 extends A {

    public String subAtt;

    public static class Builder …