demo01
Demo01：

package edu.xcdq.demo01;

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

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);
        System.out.println(list);
        // 加入泛型，做约束
        ArrayList<String> alist = new ArrayList<>();
        alist.add("111");
         // alist.add(111)；加入了泛型，不可以存储泛型之外的数据类型


    }
}

demo02
Demo02:

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<>(1.1,1.2);
        System.out.println(pair2);


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

Pair:

public class Pair <T>{  //type
    private  T first;
    private  T  second;

    //构造方法
    public Pair(){

    }
public  Pair(T first,T second){
        this.first = first;
        this.second = second;
}
    public T getFirst() {
        return first;
    }

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

    public T getSecond() {
        return second;
    }

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




    }

demo03
ArrayAlg:

public class ArrayAlg {
    // 求出所有通用的数据中间位置的值
    public  static <T> T getMiddle(T[] a){
        return a [a.length /2];
    }
}

Demo03:

public class Demo03 {
    public static void main(String[] args) {

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


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

    }
}

demo04
Canvas:

public class Canvas {
    public void draw(Shape shape){
        shape.xingzhuang();
    }
    //在画布上花多个
    public void drawAll (List<Shape> shapeList){
        for ( Shape s : shapeList){
            s.xingzhuang();
        }

    }
}

Shape:

public  abstract class Shape {

    public  abstract void xingzhuang();



}

Circle:

public class Circle extends Shape {

    public void xingzhuang(){
        System.out.println("正在画圆");
    }

}

Rectangle:

public class Rectangle extends Shape {

    public void xingzhuang(){
        System.out.println("正在矩形");
    }
}

Demo04:

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();
        Rectangle rectangle = new Rectangle();
        Rectangle rectangle1 = new Rectangle();
        Circle  circle2 = new Circle();

        ArrayList<Shape> list = new ArrayList<>();
        list.add(circle1);
        list.add(rectangle);
        list.add(rectangle1);
        list.add(circle2);
        canvas.drawAll(list);
    }
}