类型通配符

package com.czie.iot1913.lps.genericityDemo.Demo03;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

/**
 * @author 1944900433@qq.com
 * @date 2022-03-19 21:50
 */
public class genericityDemo01 {

    public static void main(String[] args) {
        List<?> list1=new ArrayList<Objects>();
        List<?> list2=new ArrayList<Number>();
        List<?> list3=new ArrayList<Integer>();
        System.out.println("==============");
        //类型通配符上限
        //ArrayList<? extends Number> list4 = new ArrayList<Objects>();
        ArrayList<? extends Number> list5 = new ArrayList<Number>();
        ArrayList<? extends Number> list6 = new ArrayList<Integer>();
        System.out.println("----------------");
        //类型通配符下限
        List<? super Number> list7=new ArrayList<Object>();
        List<? super Number> list8=new ArrayList<Number>();
        //List<? super Number> list9=new ArrayList<Integer>();
    }
}