java-使用泛型将子类生成器初始化为父类生成器的类型

Question

我在父类和子类中都有构建器。父对象有一个抽象生成器和一个扩展抽象生成器的具体生成器。子级有一个扩展父级抽象生成器的抽象生成器和一个扩展子级抽象生成器的具体生成器。原因是父级的setter返回当前的Builder类。我有一些方法返回类自己的抽象构建器类型，我想将其称为父抽象类型（调用它的父方法）。我所能做的就是ParentBuilder

我想在主代码中执行的操作：

ParentBuilder<? extends ParentBuilder<?> builder; // How to do this?
if (something) {
    builder = Child.doSomething();
}
else {
    builder = new Parent.builder();
}

Parent p = builder.setThing1("foo").build();

在Parent.java

public class Parent {

    private final String thing1;

    protected <B extends ParentBuilder<B>> Parent(final B builder) {
        this.thing1 = builder.thing1;
    }

    public String getThing1() {
        return this.thing1;
    }

    protected abstract static class ParentBuilder<B extends ParentBuilder<B>> {
        protected final Class<B> builderClass;
        protected String thing1;

        protected ParentBuilder(final Class<B> builderClass) {
            this.builderClass = builderClass;
        }

        public B setThing1(final String thing1) {
            this.thing1 = thing1;
            return builderClass.cast(this);
        }

        public abstract Parent build();
    }

    public static class Builder extends ParentBuilder<Builder> {
        public Builder() {
            super(Builder.class);
        }

        @Override
        public Parent build() {
            return new Parent(this);
        }
    }
}

在孩子身上。JAVA

public class Child extends Parent {

    private final String thing2;

    protected <B extends ChildBuilder<B>> Child(final B builder) {
        super(builder);
        this.thing2 = builder.thing2;
    }

    public String getThing2() {
        return this.thing2;
    }

    public static Builder doThings(/*...*/) {
        //...
        return new Child.Builder();
    }

    protected abstract static class ChildBuilder<B extends ParentBuilder<B>> extends ParentBuilder<B> {
        protected String thing2;

        protected ChildBuilder(final Class<B> builderClass) {
            super(builderClass);
        }

        public B setThing2(final String thing2) {
            this.thing2 = thing2;
            return builderClass.cast(this);
        }
    }

    public static class Builder extends ChildBuilder<Builder> {
        public Builder() {
            super(Builder.class);
        }

        @Override
        public Child build() {
            return new Child(this);
        }
    }
}

在第一节中，我将构建器声明为父抽象构建器类型，但我不确定键入该对象的正确方式。通配符似乎不对。我想到的一个选择是在抽象构建器之上创建一个接口，然后我可以使用这种类型。但有接口似乎很麻烦-




Answer 1

以下是您的设置的工作代码：

Parent.ParentBuilder<?> builder; 

if ( something ) {
    builder = new Child.Builder();
}
else {
    builder = new Parent.Builder();
}

Parent p = builder.setThing1("foo").build();

现在，如果您希望builder.build（）返回子而不进行强制转换，您需要更改现有的生成器泛型类型声明。