java 泛型

package com.test;

import com.czbsit.web.result.CodeMsg;

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

public class Response<T> {
    private int code;
    private String msg;
    private T data;

    private  Response( T data) {
        this.code = 0;
        this.msg = "OK";
        this.data = data;
    }
    private Response(CodeMsg codeMsg){
        this.code=codeMsg.getCode();
        this.msg=codeMsg.getMsg();
    }
    public static <T> Response<T> success(T data){
        return new Response<>(data);
    }
    public static <T> Response<T> error(CodeMsg codeMsg){
    return new Response(codeMsg);
    }

    public static void main(String[] args) {
       // Response<String> stringResponse = new Response<String>(12);//错误 new 指定泛型类型
        Response<String> stringResponse1 = new Response<String>("333");//new 指定泛型类型
        ArrayList<Integer> intArr=new ArrayList<>();
        intArr.add(12);
        intArr.add(123);
        ArrayList<String> strArr=new ArrayList<>();
        strArr.add("aa");
        strArr.add("bb");
        printArrayList(intArr);
        printArrayList(strArr);
        List<Number> list1=new ArrayList<>();
        List<Integer> list2 =new ArrayList<>();
        List<String> list23=new ArrayList<>();
        printArrayList2(list1);
        printArrayList2(list2);
        //printArrayList2(list123);//错误
    }

    public static void printArrayList(ArrayList<?> arr){//泛型通配符?使用案例
        for (int i = 0; i < arr.size(); i++) {
            System.out.println(arr.get(i));
        }
    }
    public static void printArrayList2(List<? extends Number> arr){//泛型通配符?使用案例 只能是Number本身或子类 List<? super Number>只能是Number本身或父类
        for (int i = 0; i < arr.size(); i++) {
            System.out.println(arr.get(i));
        }
    }
}

public interface IFanXingInter<T> {
    void say(T t);
}

public class FanXingInterImpl implements IFanXingInter<String> {//实现类时确定泛型类型

    @Override
    public void say(String s) {
        System.out.println(s);
    }
}