复习集合相关

复习集合相关

1.collection和List有好多相同名，但又略微不同的方法

比如Collection的add和remove返回值是bollean，而list的返回值是voidheobject。

另外collection的remove内部填写内容，而list的remove内部填写索引。

 

 2.Collection常用方法及继承结构

 

public static void main(String[] args) {
        Collection c = new ArrayList();
        //常用方法
        //1.增加 boolean add
        c.add(100);
        c.add(200);
        c.add(300);
        c.add(400);
        c.add(500);
        c.add(100);
        c.add(100);
        //2.boolean remove 这里写的是内容
        c.remove(100);
        c.remove(100);
        c.remove(100);
        //3.boolean contains
        System.out.println(c.contains(100));
        //5.void clear
        c.clear();
        //6.boolean isEmpty
        System.out.println(c.isEmpty());
    }

2.1 list常用方法及之前没有在意的知识点

public static void main(String[] args) {
        List l = new ArrayList();//初始长度为10，1.5倍扩容
        //1.增加void add
        l.add(100);
        l.add(200);
        l.add(300);
        l.add(400);
        l.add(500);
        l.add(100);
        l.add(100);
        //2.object remove注意这里写的是索引
        l.remove(1);
        //3.object get()
        System.out.println(l.get(1));
        //4.object set
        l.set(1,111);
        System.out.println(l.get(1));
    }

2.1.1 arraylist

 
        //注意直接通过构造方法可以将hashSet转化为arrayList
        HashSet h = new HashSet();
        h.add(100);
        h.add(100);
        List l = new ArrayList(h);
        for (int i = 0; i < l.size(); i++) {
            System.out.println(l.get(i));//因为hashset无序不可重复，所以只添加了一个100
        }

2.1.2 linkedlist

        List list2 = new ArrayList(); // 这样写表示底层你用了数组。
        List list3 = new linkedList(); // 这样写表示底层你用了双向链表。

2.1.3 vector

2.2map常用方法及之前没有在意的知识

 相关方法

list有set方法，添加使用的时add，而map添加和修改都通过put，因为key不可重复

Map map = new HashMap();
        //1.V put()
        map.put(1,'a');
        map.put(2,'b');
        map.put(3,'c');
        map.put(4,'d');
        //2.V get
        System.out.println(map.get(1));
        //3.void clear
        map.clear();
        //4.boolean isEmpty
        System.out.println(map.isEmpty());
        //5.boolean containsKey()和boolean containsValue
        map.put(1,'a');
        map.put(2,'b');
        map.put(3,'c');
        map.put(4,'d');
        map.put(5,'e');
        map.put(6,'f');
        map.put(7,'d');
        System.out.println("有对应的key吗"+map.containsKey(3));
        System.out.println("有对应的value吗"+map.containsValue('c'));
        //6.collection values
        System.out.println(map.values() instanceof Collection);
        //7.set keSet
        Set hs = map.keySet();
        for (Object i:hs) {
            System.out.println(i);
        }
        //8.entrySet
        Set set = map.entrySet();
        for (Object i:set) {
            System.out.print(i+" ");
        }

2.2.1

package myMap.HashMap;

public class Test01 {
    public static void main(String[] args) {
        
    }
}

2.2.2

通过实现comparable实现

package myMap.TreeMap;

import java.util.Set;
import java.util.TreeSet;


public class Test {
    public static void main(String[] args) {
        beauty biYue = new beauty("貂蝉",19,3);
        beauty xiuHua = new beauty("杨玉环",25,4);
        beauty chenYu = new beauty("西施",21,1);
        beauty luoYan = new beauty("王昭君",24,2);

        Set theFourBeauty = new TreeSet<>();
        theFourBeauty.add(biYue);
        theFourBeauty.add(xiuHua);
        theFourBeauty.add(chenYu);
        theFourBeauty.add(luoYan);
        for (beauty b:theFourBeauty) {
            System.out.println(b);
        }
    }
}

class beauty implements Comparable{
    private String name;
    private int age;
    private int popularity;

    public beauty(){}

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

    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 getPopularity() {
        return popularity;
    }

    public void setPopularity(int popularity) {
        this.popularity = popularity;
    }

    @Override
    
    public int compareTo(beauty o) {
        if (this.getPopularity() == o.getPopularity()){
            return 0;
        }else {
            return this.getPopularity() - o.getPopularity();
        }
    }

    @Override
    public String toString() {
        return "beauty{" +
                "姓名:" + name +
                "知名度:" + popularity +
                '}';
    }
}

使用比较器

package myMap.TreeMap;

import java.util.*;

public class Test02 {
    public static void main(String[] args) {
        classics xiYou = new classics(1306,1);
        classics shuiHu = new classics(1325,4);
        classics hongLou = new classics(1623,3);
        classics sanGuo = new classics(1106,2);

        TreeMap map = new TreeMap<>(new classicsComparator());
        map.put(xiYou,27);
        map.put(shuiHu,66);
        map.put(hongLou,88);
        map.put(sanGuo,49);
        Set s =  map.keySet();
        Iterator it = s.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
}

class classics{

    private int birth;
    private int popularity;

    public classics( int birth, int popularity) {

        this.birth = birth;
        this.popularity = popularity;
    }
    public classics(){}


    public int getBirth() {
        return birth;
    }

    public void setBirth(int birth) {
        this.birth = birth;
    }

    public int getPopularity() {
        return popularity;
    }

    public void setPopularity(int popularity) {
        this.popularity = popularity;
    }

    @Override
    public String toString() {
        return "classics{" +
                "birth=" + birth +
                ", popularity=" + popularity +
                '}';
    }
}

class classicsComparator implements Comparator {
    @Override
    public int compare(classics o1, classics o2) {
        return o1.getPopularity()-o2.getPopularity();
    }
}

2.2.3

2.2.4

   public static void main(String[] args) {
        // 创建对象
        Properties pro = new Properties();
        // 存
        pro.setProperty("username", "test");
        pro.setProperty("password", "test123");
        // 取
        String username = pro.getProperty("username");
        String password = pro.getProperty("password");
        System.out.println(username);
        System.out.println(password);

    }