集合相关 java（heima学习）

于 2022-04-04 16:22:58 发布
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分类专栏： Java学习 文章标签： java
版权声明：本文为博主原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。
本文链接：https://blog.youkuaiyun.com/weixin_52005267/article/details/123835126
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本文通过示例介绍了Java编程中集合的使用，包括HashSet、TreeSet的实现元素唯一性和排序，以及泛型在类、方法和接口中的应用。还展示了如何使用HashMap和TreeMap进行数据存储和遍历，以及随机数生成、字符串统计和ArrayList排序。最后，模拟了斗地主游戏的洗牌和发牌过程，展示了数据结构在实际问题中的应用。

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1、创建一个存储学生对象的集合，要求：学生对象的成员变量值相同，我们就认为是同一个对象

未重写hashCode和equals方法 的情况

package learnjava;

public class Student {
    private String name;
    private int age;

    public Student(){

    }

    public Student(String name,int age){
        this.name=name;
        this.age=age;
    }

    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;
    }
    
}

package learnjava;

import java.util.HashSet;

public class Demo {
    public static void main(String[] args) {
        HashSet<Student> hs = new HashSet<>();

        Student s1 = new Student("林青霞", 35);
        Student s2 = new Student("王祖贤", 30);

        Student s3 = new Student("王祖贤", 30);

        hs.add(s1);
        hs.add(s2);
        hs.add(s3);

        for(Student s:hs){
            System.out.println(s.getName()+","+s.getAge());
        }
//        王祖贤,30
//        王祖贤,30
//        林青霞,35
    }
}

为保证元素唯一性，应重写hashCode和equals方法

package learnjava;

public class Student {
    private String name;
    private int age;

    public Student(){

    }

    public Student(String name,int age){
        this.name=name;
        this.age=age;
    }

    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;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Student student = (Student) o;

        if (age != student.age) return false;
        return name != null ? name.equals(student.name) : student.name == null;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }
}

package learnjava;

import java.util.HashSet;

public class Demo {
    public static void main(String[] args) {
        HashSet<Student> hs = new HashSet<>();

        Student s1 = new Student("林青霞", 35);
        Student s2 = new Student("王祖贤", 30);

        Student s3 = new Student("王祖贤", 30);

        hs.add(s1);
        hs.add(s2);
        hs.add(s3);

        for(Student s:hs){
            System.out.println(s.getName()+","+s.getAge());
        }
//        林青霞,35
//        王祖贤,30
    }
}

2、存储学生对象并遍历，创建集合使用无参构造方法，
要求：按照年龄从大到小排序，年龄相同时，按照姓名的字母顺序排序

自然排序Comparable的使用：自定义类implements Comparable接口，并重写compareTo(To)方法

TreeSet有序

package learnjava;

public class Student implements Comparable<Student> {
    private String name;
    private int age;

    public Student(){

    }

    public Student(String name,int age){
        this.name=name;
        this.age=age;
    }

    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;
    }

    @Override
    public int compareTo(Student s){
        int n1=this.age-s.age;//this-s 为升序
        int n2=(n1==0)?this.name.compareTo(s.name):n1;
        return n2;
    }
}

package learnjava;

import java.util.TreeSet;

public class Demo {
    public static void main(String[] args) {
        TreeSet<Student> hs = new TreeSet<>();

        Student s1 = new Student("lin", 35);
        Student s2 = new Student("wang", 30);
        Student s3 = new Student("zhang", 36);
        Student s4 = new Student("feng", 30);

        hs.add(s1);
        hs.add(s2);
        hs.add(s3);
        hs.add(s4);

        for(Student s:hs){
            System.out.println(s.getName()+","+s.getAge());
        }
//        feng,30
//        wang,30
//        lin,35
//        zhang,36
    }
}

3、存储学生对象并遍历，创建TreeSet集合使用带参构造方法，
要求：按照年龄从大到小排序，年龄相同时，按照姓名的字母顺序排序

Comparator的使用，让集合构造方法接收Comparator的实现类对象，重写compare(T o1,T o2)

package learnjava;

public class Student  {
    private String name;
    private int age;

    public Student(){

    }

    public Student(String name,int age){
        this.name=name;
        this.age=age;
    }

    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;
    }
}

package learnjava;

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

public class Demo {
    public static void main(String[] args) {
        TreeSet<Student> hs = new TreeSet<>(new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                int n1=s1.getAge()-s2.getAge();
                int n2=(n1==0)?s1.getName().compareTo(s2.getName()):n1;
                return n2;
            }
        });

        Student s1 = new Student("lin", 35);
        Student s2 = new Student("wang", 30);
        Student s3 = new Student("zhang", 36);
        Student s4 = new Student("feng", 30);

        hs.add(s1);
        hs.add(s2);
        hs.add(s3);
        hs.add(s4);

        for(Student s:hs){
            System.out.println(s.getName()+","+s.getAge());
        }
//        feng,30
//        wang,30
//        lin,35
//        zhang,36
    }
}

4、获取10个 1-20之间的随机数，要求随机数不能重复

package learnjava;

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

public class Demo {
    public static void main(String[] args) {
        Set<Integer> set = new HashSet<>();

        Random r=new Random();
        int x=0;

        for(int i=0;i<10;i++){
            x=r.nextInt(20)+1;
            set.add(x);
        }

        for(int num:set){
            System.out.println(num);
        }
//        16
//        19
//        3
//        9
//        10
//        13
//        14
    }
}

5、泛型类：

package learnjava;

public class Generic<T> {
    private T t;
    public T getT(){
        return t;
    }
    public void setT(T t){
        this.t=t;
    }
}

package learnjava;

public class Demo {
    public static void main(String[] args) {
        Generic<String> g1=new Generic<>();
        g1.setT("林青霞");

        Generic<Integer> g2=new Generic<>();
        g2.setT(100);

        System.out.println(g1.getT());
        System.out.println(g2.getT());
        //林青霞
        //100
    }
}

6、泛型方法：

package learnjava;

public class Generic {
    public <T> void show(T t){
        System.out.println(t);
    }
}


package learnjava;

public class Demo {
    public static void main(String[] args) {
        Generic g=new Generic();
        g.show("林青霞");

        g.show(100);

        //林青霞
        //100
    }
}

7、泛型接口：

package learnjava;

public interface Generic<T> {
    void show(T t);
}

package learnjava;

public class GenericImpl<T> implements Generic<T>{
    @Override
    public void show(T t){
        System.out.println(t);
    }
}

package learnjava;

public class Demo {
    public static void main(String[] args) {
        Generic g=new GenericImpl();
        g.show("林青霞");

        g.show(100);

        //林青霞
        //100
    }
}

8、Map集合的遍历：

package learnjava;

import java.util.HashMap;
import java.util.Map;

public class Demo {
    public static void main(String[] args) {
        Map<String,String> map=new HashMap<>();

        map.put("二郎神","嫦娥");
        map.put("程琉","季朝舟");
        map.put("白柳","塔维尔");
        
        //法一
        for(String key:map.keySet()){
            System.out.println(key+","+map.get(key));
        }
        System.out.println();

        //法二
        for(Map.Entry<String,String> entry:map.entrySet()){
            System.out.println(entry.getKey()+","+entry.getValue());
        }
        //程琉,季朝舟
        //二郎神,嫦娥
        //白柳,塔维尔
        //
        //程琉,季朝舟
        //二郎神,嫦娥
        //白柳,塔维尔
    }
}

9、统计字符串中每个字符出现的次数

package learnjava;

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Demo {
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        String s=in.nextLine();
        Map<Character,Integer> map=new HashMap<>();
        char key;
        Integer value;

        for(int i=0;i<s.length();i++){
            key=s.charAt(i);
            value=map.get(key);
            if(value==null){
                map.put(key,1);
            }else {
                value++;
                map.put(key,value);
            }
        }

        StringBuilder sb=new StringBuilder();
        for(Character c:map.keySet()){
            sb.append(c).append("(").append(map.get(c)).append(")");
        }

        String res=sb.toString();
        System.out.println(res);
    }
}
//aababcabcdabcde
//a(5)b(4)c(3)d(2)e(1)

10、ArryList存储学生对象并排序

package learnjava;

public class Student  {
    private String name;
    private int age;

    public Student(){

    }

    public Student(String name,int age){
        this.name=name;
        this.age=age;
    }

    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;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Student student = (Student) o;

        if (age != student.age) return false;
        return name != null ? name.equals(student.name) : student.name == null;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }
}


package learnjava;

import java.util.*;

public class Demo {
    public static void main(String[] args) {
        ArrayList<Student> array=new ArrayList<>();
        Student s1 = new Student("lin", 35);
        Student s2 = new Student("wang", 30);
        Student s3 = new Student("zhang", 36);
        Student s4 = new Student("feng", 30);

        array.add(s1);
        array.add(s2);
        array.add(s3);
        array.add(s4);

        Collections.sort(array, new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                int n1=s1.getAge()-s2.getAge();
                int n2=(n1==0)?s1.getName().compareTo(s2.getName()):n1;
                return n2;
            }
        });
    }
}

11、模拟斗地主案例
洗牌洗的是牌的编号，发牌也是按编号发，以便从小到大为牌排序（TreeMap）

package learnjava;

import java.util.*;

public class Demo {
    public static void main(String[] args) {
        String[] colors={"♦","♣","♥","♠"};
        String[] numbers={"3","4","5","6","7","8","9","10","J","Q","K","A","2"};
        HashMap<Integer,String> map=new HashMap<>();//牌的编号，具体牌
        ArrayList<Integer> array=new ArrayList<>();//存储牌的编号

        int index=0;

        for(String number:numbers){
            for (String color:colors){
                map.put(index,color+number);
                array.add(index);
                index++;
            }
        }
        map.put(index,"小王");
        index++;
        map.put(index,"大王");

        Collections.shuffle(array);//洗牌

        TreeSet<Integer> first=new TreeSet<>();//第一个人获得的所有牌的编号
        TreeSet<Integer> second=new TreeSet<>();
        TreeSet<Integer> third=new TreeSet<>();
        TreeSet<Integer> dipai=new TreeSet<>();//底牌

        for(int i=0;i<array.size();i++){//发牌
            int x= array.get(i);
            if(i>= array.size()-3){
                dipai.add(x);
            }else if(x%3==0){
                first.add(x);
            }else if(x%3==1){
                second.add(x);
            }else {
                third.add(x);
            }
        }

        lookPoker("林青霞",first,map);
        lookPoker("张曼玉",second,map);
        lookPoker("王祖贤",third,map);
        lookPoker("底牌",dipai,map);
    }
    public static void lookPoker(String name,TreeSet<Integer> t,HashMap<Integer,String> hm){
        System.out.print(name+"的牌是：");
        for(Integer key:t){
            System.out.print(hm.get(key)+" ");
        }
        System.out.println();
    }
    //林青霞的牌是：♦3 ♠3 ♥4 ♣5 ♠6 ♥7 ♣8 ♦9 ♠9 ♥10 ♣J ♦Q ♠Q ♥K ♣A ♦2 ♠2 
    //张曼玉的牌是：♣3 ♦4 ♠4 ♣6 ♦7 ♠7 ♥8 ♣9 ♦10 ♠10 ♥J ♦K ♠K ♥A ♣2 
    //王祖贤的牌是：♥3 ♣4 ♦5 ♠5 ♥6 ♣7 ♦8 ♠8 ♥9 ♣10 ♦J ♠J ♥Q ♣K ♦A ♠A ♥2 
    //底牌的牌是：♥5 ♦6 ♣Q 
}
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