demo01

Demo01

package demo01;

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

//泛型的使用
public class Demo01 {

    public static void main(String[] args) {
        //为了解决通用性的问题，jdk提供了封装好的集合，但是集合可以存放不同类型的数据
        List list = new ArrayList();
        list.add("111");
        list.add(111);
        list.add(true);
        list.add(11.1);

        //加入泛型，做约束
        ArrayList<String> alist = new ArrayList<>();
        alist.add("111");
        //alist.add("111");加入泛型，不可储存泛型之外的数据类型
    }
}

demo02

Demo02

package demo02;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 15:23
 */
public class Demo02 {
    public static void main(String[] args) {
        Pair<Integer> pair1 = new Pair<>(1, 2);
        System.out.println(pair1);

        Pair<Double> pair2 = new Pair<>(1.1, 2.2);
        System.out.println(pair2);

        Pair<String> pair3 = new Pair<>("haha", "hehe");
        System.out.println(pair3);
    }
}

Pair

package demo02;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 15:20
 */
public class Pair<T> {
    private T first ;
    private T second ;
    //构造方法
    public Pair(){
    }
    public Pair(T first, T second){
        this.first = first;
        this.second = second ;
    }
    //setter & getter
    public T getFirst() {
        return first;
    }

    public T getSecond() {
        return second;
    }

    public void setFirst(T first) {
        this.first = first;
    }

    public void setSecond(T second) {
        this.second = second;
    }

    @Override
    public String toString() {
        return "Pair{" +
                "first=" + first +
                ", second=" + second +
                '}';
    }
}

demo03

Demo03

package demo03;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 15:33
 */
public class Demo03 {
    public static void main(String[] args) {
        Integer[] a = {1,2,3,4,5,6};
        System.out.println(AeeayAlg.getMiddle(a));

        Integer[] b = {1,2,3,4,5};
        System.out.println(AeeayAlg.getMiddle(b));

        String[] str = {"111","222","333","444"};
        System.out.println(AeeayAlg.getMiddle(str));

        String[] str1 = {"111","222","333","444"};
    }
}

AeeayAlg

package demo03;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 15:34
 */
public class AeeayAlg {
    //数组相关算法，求出通用的数据中间位置的值
    public static <T> T getMiddle(T[] a){
        return  a[a.length/2];
    }
}

demo04

Demo04

package demo04;

import java.awt.*;
import java.util.ArrayList;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 16:06
 */
public class Demo04 {
    public static void main(String[] args) {
        Canvas canvas = new Canvas();
        Circle circle =new Circle();
        canvas.draw(circle);

        //定义多个形状，组成一个数组列表，传入
        Circle circle1 =new Circle();
        Rectabgle rectabgle = new Rectabgle();
        Rectabgle rectabgle1 = new Rectabgle();

//        Rectabgle rectangle =new Rectangle();
//        Rectabgle rectangle1 = new Rectangle();
        Circle circle2 =new Circle();
        //准备一个集合
        ArrayList<Shape>list = new ArrayList<>();
        list.add(circle);
        list.add(circle1);
        list.add(circle2);
        list.add(rectabgle);
        list.add(rectabgle1);
        canvas.drawAll(list);
    }
}

Canvas

package demo04;

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

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 16:03
 */
public class Canvas {
    // 在画布上画的一个
    public void draw(Shape shape){
        shape.xingzhuang();
    }
    // 在画布上画多个
    public void drawAll(List< ? extends Shape >shapeList){
        for (Shape s : shapeList){
            s.xingzhuang();
        }
    }
    public void drawAll(ArrayList<Shape> list) {
    }
}

Circle

package demo04;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 16:02
 */
public class Circle extends Shape{
    @Override
    public void xingzhuang() {
        System.out.println("正在画圆");
    }
}

Rectabgle

package demo04;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 16:14
 */
public class Rectabgle extends Shape{
    @Override
    public void xingzhuang(){
        System.out.println("正在画矩形");
    }
}

Shape

package demo04;

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 16:00
 */
public abstract class Shape {
    public abstract void xingzhuang();
}

demo05

Demo05

package demo05;

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

/**
 * @qvthor liuwenzheng
 * @date 2021/5/11 16:27
 */
public class Demo05 {
    public static void main(String[] args) {
        ArrayList<Object> list = new ArrayList<>();
        List tempList = list ; // 泛型的擦除
        tempList.add(1213);
        System.out.println(tempList);
    }
}