集合实例练习

Posted 2020-11-04

1、键盘录入5个学生信息(姓名,语文成绩,数学成绩,英语成绩),按照总分从高到低输出到控制台。
a:自然排序
测试类：
`package treeSet集合;

import java.util.Comparator;
import java.util.Scanner;
import java.util.TreeSet;

public class ZuoyeScannerSelect {
public static void main(String[] args) {
TreeSet<StudentSelect> ts=new TreeSet<StudentSelect>(new Comparator<StudentSelect>() {

        @Override
        public int compare(StudentSelect s1, StudentSelect s2) {
            int num1=s2.sum(s2)-s1.sum(s1);
            int num2=(num1==0)?s2.getName().compareTo(s1.getName()):num1;
            return num2;
        }

    }) ;
    System.out.println("请输入学生信息:");
    //录入学生信息
    for(int x=1;x<6;x++) {
        Scanner sc=new Scanner(System.in);
        System.out.print("请输入第"+x+"个学生的姓名:");
        //录入学生姓名
        String name=sc.nextLine();
        System.out.print("请输入第"+x+"个学生的语文成绩:");
        //录入学生语文成绩
        int chineseScore=sc.nextInt();
        System.out.print("请输入第"+x+"个学生的数学成绩:");
        //录入学生数学成绩
        int mathScore=sc.nextInt();
        System.out.print("请输入第"+x+"个学生的英语成绩:");
        //录入学生英语成绩
        int englishScore=sc.nextInt();
        //将学生信息封装到学生对象里
        StudentSelect s=new StudentSelect();
        s.setName(name);
        s.setChineseScore(chineseScore);
        s.setMathScore(mathScore);
        s.setEnglishScore(englishScore);
        //把学生对象添加到集合中
        ts.add(s);
    }
    //遍历
    for(StudentSelect s:ts) {
        System.out.println(s.getName()+","+ + s.getChineseScore()+","
    + s.getMathScore()+","+ s.getEnglishScore()+","+s.sum(s));
    }
}   

}`
实体类：

package treeSet集合;

public class StudentZiran implements Comparable<StudentZiran>{
    //自然排序,自定义类中实现Comparable接口
    private String name;
    private int chineseScore;
    private int mathScore;
    private int englishScore;

    public StudentZiran() {//无参构造
        // TODO Auto-generated constructor stub
    }
    //有参构造
    public StudentZiran(String name,int chineseScore,int mathScore,int englishScore) {
        this.name=name;
        this.chineseScore=chineseScore;
        this.mathScore=mathScore;
        this.englishScore=englishScore;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getChineseScore() {
        return chineseScore;
    }
    public void setChineseScore(int chineseScore) {
        this.chineseScore = chineseScore;
    }
    public int getMathScore() {
        return mathScore;
    }
    public void setMathScore(int mathScore) {
        this.mathScore = mathScore;
    }
    public int getEnglishScore() {
        return englishScore;
    }
    public void setEnglishScore(int englishScore) {
        this.englishScore = englishScore;
    }
    //求总成绩方法
    public  int sum(StudentZiran s) {
        return s.getChineseScore()+s.getMathScore()+s.getEnglishScore();
    }
    //重写compearTo()方法
    @Override
    public int compareTo(StudentZiran s) {
        //主要排序条件:总成绩,按总成绩从高到低
        int num1=s.sum(s)-this.sum(this);
        //次要排序条件,当总成绩相同时按学生姓名内容比较
        int num2=(num1==0)?s.getName().compareTo(this.getName()):num1;
        return num2;
    }   
}

    b:选择器排序
    测试类：
    `package treeSet集合;

import java.util.Comparator;
import java.util.Scanner;
import java.util.TreeSet;

public class ZuoyeScannerSelect {
public static void main(String[] args) {
TreeSet<StudentSelect> ts=new TreeSet<StudentSelect>(new Comparator<StudentSelect>() {

        @Override
        public int compare(StudentSelect s1, StudentSelect s2) {
            int num1=s2.sum(s2)-s1.sum(s1);
            int num2=(num1==0)?s2.getName().compareTo(s1.getName()):num1;
            return num2;
        }

    }) ;
    System.out.println("请输入学生信息:");
    //录入学生信息
    for(int x=1;x<6;x++) {
        Scanner sc=new Scanner(System.in);
        System.out.print("请输入第"+x+"个学生的姓名:");
        //录入学生姓名
        String name=sc.nextLine();
        System.out.print("请输入第"+x+"个学生的语文成绩:");
        //录入学生语文成绩
        int chineseScore=sc.nextInt();
        System.out.print("请输入第"+x+"个学生的数学成绩:");
        //录入学生数学成绩
        int mathScore=sc.nextInt();
        System.out.print("请输入第"+x+"个学生的英语成绩:");
        //录入学生英语成绩
        int englishScore=sc.nextInt();
        //将学生信息封装到学生对象里
        StudentSelect s=new StudentSelect();
        s.setName(name);
        s.setChineseScore(chineseScore);
        s.setMathScore(mathScore);
        s.setEnglishScore(englishScore);
        //把学生对象添加到集合中
        ts.add(s);
    }

    //遍历
    for(StudentSelect s:ts) {
        System.out.println(s.getName()+","+ + s.getChineseScore()+","
    + s.getMathScore()+","+ s.getEnglishScore()+","+s.sum(s));
    }
}   

}`
实体类：

package treeSet集合;

public class StudentSelect {
    private String name;
    private int chineseScore;
    private int mathScore;
    private int englishScore;

    public StudentSelect() {//无参构造
        // TODO Auto-generated constructor stub
    }
    //有参构造
    public StudentSelect(String name,int chineseScore,int mathScore,int englishScore) {
        this.name=name;
        this.chineseScore=chineseScore;
        this.mathScore=mathScore;
        this.englishScore=englishScore;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getChineseScore() {
        return chineseScore;
    }
    public void setChineseScore(int chineseScore) {
        this.chineseScore = chineseScore;
    }
    public int getMathScore() {
        return mathScore;
    }
    public void setMathScore(int mathScore) {
        this.mathScore = mathScore;
    }
    public int getEnglishScore() {
        return englishScore;
    }
    public void setEnglishScore(int englishScore) {
        this.englishScore = englishScore;
    }
    //求总成绩方法
    public static int sum(StudentSelect s) {
        return s.getChineseScore()+s.getMathScore()+s.getEnglishScore();
    }

}

2、获取10随机数,1-20之间,要求值不能重复!(ArrayList,HashSet)
ArrayList：

package 集合获取随机数;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;

public class ArrayListGetRandom {
    public static void main(String[] args) {
        //创建集合al
        ArrayList<Integer> al=new ArrayList<Integer>();
        //创建新集合newal
        ArrayList<Integer> newal=new ArrayList<Integer>();
        //判断新集合newal中的元素个数是否够10个,若不够,继续添加
        while(newal.size()<10) {
            //创建获取随机数对象
            Random r=new Random();
            //获取随机数
            int n=r.nextInt(20);
            //将获取到的随机数添加到集合al集合
            al.add(n);
            //遍历旧集合
            Iterator<Integer> it=al.iterator();
            while(it.hasNext()) {
               int i=it.next();
               //判断newal中是否包含al中的元素,若不包含,将al中的元素添加到newal中
               if(!newal.contains(i)) {
                   newal.add(i);
               }
            }
            //遍历newal集合
            for(int i:newal) {
               System.out.println(i);
            }
        }
    }
}

HashSet：

package 集合获取随机数;

import java.util.HashSet;
import java.util.Random;
import java.util.Set;

public class HashSetGetRandom {
    public static void main(String[] args) {
        //创建Set集合对象
        Set<Integer> set=new HashSet<Integer>();
        //创建获取随机数类对象
        Random r=new Random();
        //判断已获取随机数个数,若不够10个,则继续添加
        while(set.size()<10) {
            //获取随机数
            int n=r.nextInt(20);
              //将获取的随机数添加到集合set中
              set.add(n);      
        }
        //增强for循环遍历集合set
        for(int i:set) {
             System.out.println(i);
        }
    }
}

3、ArrayList集合嵌套HashMap集合并遍历。
需求：
假设ArrayList集合的元素是HashMap。有3个。
每一个HashMap集合的键和值都是字符串。
元素如下，请遍历。

ArrayList<HashMap<String,String>>

结果：
周瑜---小乔
吕布---貂蝉

郭靖---黄蓉
杨过---小龙女

令狐冲---任盈盈
林平之---岳灵珊
`package 集合嵌套;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Set;

public class AM {
public static void main(String[] args) {
//创建一个大的ArrayList集合am
ArrayList<HashMap<String,String>> am=new ArrayList<HashMap<String,String>>();
//创建第一个HashMap集合hm1
HashMap<String,String> hm1=new HashMap<String,String>();
//给集合hm1添加元素
hm1.put("周瑜","小乔");
hm1.put("吕布","貂蝉");
//将hm1的元素添加到大集合am中
am.add(hm1);
//创建第二个HashMap集合hm2
HashMap<String,String> hm2=new HashMap<String,String>();
//给集合hm2添加元素
hm2.put("郭靖","黄蓉");
hm2.put("杨过","小龙女");
//将hm2的元素添加到大集合am中
am.add(hm2);
//创建第三个HashMap集合hm3
HashMap<String,String> hm3=new HashMap<String,String>();
//给集合hm3添加元素
hm3.put("令狐冲","任盈盈");
hm3.put("林平之","岳灵珊");
//将hm3的元素添加到大集合am中
am.add(hm3);
//遍历大集合am
for(HashMap<String,String> ahm:am) {
Set<String> set=ahm.keySet();
for(String key:set) {
String value=ahm.get(key);
System.out.println(key+"---"+value);
}
System.out.println();
}
}
}`