Collections工具类和ORM思想(对象关系映射)并且使用两种方法实现

Collections是一个工具类，而Collection是一个接口，Collections帮助我们对Set,List,Map进行排序，查找，填充的辅助方法

package cn.com.collection;

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

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

        //Collection是一个接口，而Collectios是一个工具类
        List<String> s = new ArrayList<>();
        for (int i = 0; i <5; i  ) {
            s.add("小红：" i);
        }
        System.out.println(s);
        //随机排列元素
        Collections.shuffle(s);
        System.out.println(s);
        //逆序
        Collections.reverse(s);
        System.out.println(s);
        //排序
        Collections.sort(s);
        System.out.println(s);
        System.out.println(Collections.binarySearch(s,"小红：4"));
        //用特定的对象重写整个容器
        Collections.fill(s," i love you");
        System.out.println(s);
    }
}

表格存储数据，Map和List结合存储表格，也就是ORM的思想，对象关系映射

package cn.com.collection;

import java.util.*;

public class TestStoreData {
    public static void main(String[] args) {
        //测试表格数据的存储，ORM的思想 对象关系映射
        Map<String,Object> map1 = new HashMap<>();
        map1.put("id",100);
        map1.put("姓名","小红");
        map1.put("年龄",18);
        map1.put("薪水",2000);
        map1.put("入职日期","2018.9.1");

        Map<String,Object> map2 =new HashMap<>();
        map2.put("id",200);
        map2.put("姓名","小亮");
        map2.put("年龄",16);
        map2.put("薪水",1500);
        map2.put("入职日期","2016.3.3");

        Map<String,Object> map3 = new HashMap<>();
        map3.put("id",300);
        map3.put("姓名","小军");
        map3.put("年龄",17);
        map3.put("薪水",3500);
        map3.put("入职日期","2008.5.1");

        Map<String,Object> map4 = new HashMap<>();
        map4.put("id",400);
        map4.put("姓名","小琪");
        map4.put("年龄",20);
        map4.put("薪水",2000);
        map4.put("入职日期","2008.6.1");

        Map<String,Object> map5 = new HashMap<>();
        map5.put("id",500);
        map5.put("姓名","小明");
        map5.put("年龄",19);
        map5.put("薪水",1000);
        map5.put("入职日期","2019.10.1");

        List<Map<String,Object>> list = new LinkedList<>();
        list.add(map1);
        list.add(map2);
        list.add(map3);
        list.add(map4);
        list.add(map5);
//        Iterator()遍历
        for (Map<String,Object> aa:list) {
            Set<Map.Entry<String,Object>> a = aa.entrySet();
            for (Iterator<Map.Entry<String,Object>> iter = a.iterator(); iter.hasNext(); ) {
                Map.Entry<String,Object> tmp = iter.next();
                System.out.print(tmp "\t");
            }
            System.out.println();
        }
//        for (Map<String,Object> bb: list) {
//            Set<String> a = bb.keySet();
//            for (Iterator<String> c = a.iterator();c.hasNext() ;) {
//                String tmp = c.next();
//                System.out.print(tmp ":" bb.get(tmp) "\t");
//            }
//            System.out.println();
//        }
    }
}

表格存储数据：javabean和List/Map结合存储表格，也是使用ORM的思想，对象关系映射

package cn.com.collection;

import java.util.*;

public class TestSortData2 {
    public static void main(String[] args) {
        Persion p1 = new Persion(100,"小红",18,2000,"2019.8.12");
        Persion p2 = new Persion(200,"小明",19,1500,"2016.5.20");
        Persion p3 = new Persion(300,"小花",16,3600,"2020.1.1");
        Persion p4 =new Persion(400,"小军",20,4500,"2018.9.9");
//        List<Persion> list = new LinkedList<>();
//        list.add(p1);
//        list.add(p2);
//        list.add(p3);
//        list.add(p4);
//        for (Persion p : list) {
//            System.out.println(p);
//        }
        Map<Integer,Persion> m = new HashMap<>();
        m.put(100,p1);
        m.put(200,p2);
        m.put(300,p3);
        m.put(400,p4);
//        Set<Map.Entry<Integer,Persion>> a = m.entrySet();
//        for (Iterator<Map.Entry<Integer,Persion>> b =  a.iterator();b.hasNext() ; ) {
//            Map.Entry<Integer,Persion> tmp= b.next();
//            System.out.println(tmp);
//        }
        Set<Integer> xx = m.keySet();
        for (Iterator<Integer> z = xx.iterator();z.hasNext();) {
            Integer tmp = z.next();
            System.out.println(tmp "======" m.get(tmp));
        }
    }
}
class Persion {
    private int id;
    private String name;
    private int age;
    private int salary;
    private String indate;

    //要有默认的无参构造器
    public Persion() {

    }
    public int getId() {
        return id;
    }

    public Persion(int id, String name, int age, int salary, String indate) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.salary = salary;
        this.indate = indate;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getSalary() {
        return salary;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }

    public String getIndate() {
        return indate;
    }

    public void setIndate(String indate) {
        this.indate = indate;
    }

    @Override
    public String toString() {
        return "id:" id ",姓名：" name ",年龄：" age ",薪水：" salary ",入职日期：" indate;
    }
}

来源：https://www./content-4-388301.html