//.addList1(new ArrayList<String>())如何去掉这两个斜杠

Question

求问 返回类型如何变成内部类类型。
@SuppressWarnings("unused")
public static void main(String[] args) {
List<String> l = new ArrayList<String>(){
private static final long serialVersionUID = -5162194221267685944L;
public List<String> addList(List<String> list ){
this.addAll(new TreeSet<String>(list){
private static final long serialVersionUID = 603932641888586401L;
{
System.out.println(this.getClass());
}
@Override
public Comparator<? super String> comparator() {
return super.comparator();
}
});
return this;
// return Class.forName(this.getClass().toString())this;
}
public List<String> addList1(List<String> list ){
this.addAll(new TreeSet<String>(new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o1.compareTo("");
}
}){
private static final long serialVersionUID = -603932641888586401L;
});
return this;
}
{
System.out.println(this.getClass());
}
}.addList(new ArrayList<String>())
// .addList1(new ArrayList<String>())
;

}

Answer 1

我来也！问题一：匿名类无法多继承，你需要合成一个公共接口，因为只有通过这个接口才可以暴露出你想使用的addList1，参见ExtraArrayList
问题二：你需要了解下逆变的概念，顺便协变也可以了解下，参见addList方法的返回值
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.TreeSet;
public class Main {

@SuppressWarnings("unused")
    public static void main(String[] args) {
        List<String> l = new ExtraArrayList<String>() {
            private static final long serialVersionUID = -5162194221267685944L;
            public ExtraArrayList<String> addList(List<String> list) { // Contravariant is used
                this.addAll(new TreeSet<String>(list){
                    private static final long serialVersionUID = 603932641888586401L;
                    {
                        System.out.println(this.getClass());
                    }
                    @Override
                    public Comparator<? super String> comparator() {
                        return super.comparator();
                    }
                });
                return this;
//              return Class.forName(this.getClass().toString())this;
            }
            public List<String> addList1(List<String> list ){
                this.addAll(new TreeSet<String>(new Comparator<String>() {
                    public int compare(String o1, String o2) {
                        return o1.compareTo("");
                    }
                }){
                    private static final long serialVersionUID = -603932641888586401L;
                });
                return this;
            }
        {
            System.out.println(this.getClass());
        }
        }.addList(new ArrayList<String>())
        .addList1(new ArrayList<String>())
        ;
         
    }
}
interface ExtraListMethod<T> {
public List<T> addList1(List<String> list);
}
abstract class ExtraArrayList <T> extends ArrayList<T> implements ExtraListMethod<T> {
private static final long serialVersionUID = 1494777471260167L;
}

Answer 2

明白你的做法，你这样就是给匿名类一个名字。
在不给名字的情况下，如何使用反射让addList返回类型变成匿名类？

Answer 3

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.TreeSet;public class Main2 {

@SuppressWarnings("unused")
    public static void main(String[] args) throws Exception {
        List<String> l = new ArrayList<String>() {
            private static final long serialVersionUID = -5162194221267685944L;
            public List<String> addList(List<String> list) { // Contravariant is used
                this.addAll(new TreeSet<String>(list){
                    private static final long serialVersionUID = 603932641888586401L;
                    {
                        System.out.println(this.getClass());
                    }
                    @Override
                    public Comparator<? super String> comparator() {
                        return super.comparator();
                    }
                });
                return this;
//              return Class.forName(this.getClass().toString())this;
            }
            public List<String> addList1(List<String> list ){
                this.addAll(new TreeSet<String>(new Comparator<String>() {
                    public int compare(String o1, String o2) {
                        return o1.compareTo("");
                    }
                }){
                    private static final long serialVersionUID = -603932641888586401L;
                });
                return this;
            }
        {
            System.out.println(this.getClass());
        }
        }.addList(new ArrayList<String>())
        //.addList1(new ArrayList<String>())
        ;
        Method m = l.getClass().getMethod("addList1", List.class);
        m.invoke(l, new ArrayList<String>());
    }
}

Answer 4

匿名类型的方法签名完全取决于父类型，无论它内部定义多少public成员，我们都是无法访问的。除非你为这些public成员定义相应的访问接口，通过访问接口来进行访问。