集合之Map家族的TreeMap + Sort +Properties及Collections工具类和总结

桃扇骨 2024-04-20 11:18 62阅读 0赞

## 集合之Map家族的TreeMap + Sort +Properties及Collections工具类和总结 ##

### 一、TreeMap ###

#### 1.TreeMap的使用 ####

import java.util.Arrays;
    import java.util.Collection;
    import java.util.Map.Entry;
    import java.util.Set;
    import java.util.TreeMap;
    
    public class Test01 {
        
    
    	public static void main(String[] args) {
        
    		
    		TreeMap<String, Integer> map = new TreeMap<>();
    		
    		//添加元素 -- 如果key是第一次添加，则返回null
    		Integer put1 = map.put("张飞", 19);
    		Integer put2 = map.put("关羽", 20);
    		Integer put3 = map.put("刘备", 23);
    		Integer put4 = map.put("诸葛亮", 19);
    		Integer put5 = map.put("赵云", 22);
    		Integer put6 = map.put("马超", 21);
    		
    		System.out.println("put()的返回值：" + put1);
    		System.out.println("put()的返回值：" + put2);
    		System.out.println("put()的返回值：" + put3);
    		System.out.println("put()的返回值：" + put4);
    		System.out.println("put()的返回值：" + put5);
    		System.out.println("put()的返回值：" + put6);
    		
    		//替换元素，返回被替换掉的值
    		Integer put = map.put("关羽", 22);
    		System.out.println("put()的返回值：" + put);
    		
    		//替换元素，返回被替换掉的值
    		Integer replace = map.replace("关羽",25);
    		System.out.println("repace()的返回值：" + replace);
    		
    		//替换元素，返回是否替换成功的boolean
    		boolean bool = map.replace("马超",21,23);
    		System.out.println("替换元素，返回是否替换成功的boolean：" + bool);
    		
    		//清空所有元素
    		//map.clear();
    		
    		System.out.println("判断map中是否有指定的key：" + map.containsKey("刘备"));
    		System.out.println("判断map中是否有指定的value：" + map.containsValue(23));
    		
    		//获取指定key对应的value
    		Integer integer = map.get("诸葛亮");
    		System.out.println("获取指定key对应的value：" + integer);
    		
    		//获取指定key对应的value，如果没key，就返回默认值
    		Integer orDefault = map.getOrDefault("关羽", 666);
    		System.out.println("获取指定key对应的value：" + orDefault);
    		
    		System.out.println("判断map集合中是否不包含元素：" + map.isEmpty());
    		
    		//将newMap中所有的元素都添加到map中
    		TreeMap<String, Integer> newMap = new TreeMap<>();
    		
    		newMap.put("aa",10);
    		newMap.put("bb",30);
    		newMap.put("cc",20);
    		map.putAll(newMap);
    		
    		//如果map中没有该key就添加，如果有就返回对应的value
    		Integer putIfAbsent = map.putIfAbsent("ddd", 40);
    		System.out.println("如果map中没有该key就添加，如果有就返回对应的value：" + putIfAbsent);
    		
    		//根据key删除映射关系
    		map.remove("赵云");
    		//根据key+value删除映射关系
    		map.remove("cc", 20);
    		
    		System.out.println("获取map中映射关系的个数：" + map.size());
    		
    		//获取map中所有的value，返回集合
    		Collection<Integer> values = map.values();
    		System.out.println(Arrays.toString(values.toArray()));
    		
    		System.out.println("---------------");
    		
    		//遍历方式1 -- keySet()
    		//思路：获取map中所有的key，将key存放在set集合中，遍历set集合将key取出，就可以通过map获取key对应的value
    		Set<String> keySet = map.keySet();
    		for (String key : keySet) {
        
    			Integer value = map.get(key);//传入key获取到对应的value
    			System.out.println(key + " -- " + value);
    		}
    		
    		System.out.println("---------------");
    		
    		//遍历方式2 -- entrySet()
    		//entry：表示映射关系（key + value）
    		//思路：获取map中所有的映射关系对象，将映射关系对象存放在set集合中，遍历set集合将映射关系对象取出，就可以通过映射关系对象获取到key和value
    		Set<Entry<String, Integer>> entrySet = map.entrySet();
    		for (Entry<String, Integer> entry : entrySet) {
        
    			String key = entry.getKey();
    			Integer value = entry.getValue();
    			System.out.println(key + " -- " + value);
    		}
    	}
    }

#### 2.验证TreeMap的特点 ####

##### 特点：针对于Key的自然排序 #####

import java.util.Map.Entry;
    import java.util.Set;
    import java.util.TreeMap;
    
    public class Test02 {
        
    
    	public static void main(String[] args) {
        
    		
    		TreeMap<String, Integer>  map = new TreeMap<>();
    		
    		map.put("c",10);
    		map.put("d",40);
    		map.put("a",20);
    		map.put("b",30);
    		map.put("d",50);
    		
    		Set<Entry<String, Integer>> entrySet = map.entrySet();
    		
    		for (Entry<String, Integer> entry : entrySet) {
        
    			String key = entry.getKey();
    			Integer value = entry.getValue();
    			System.out.println(key + "-----" + value);
    		}
    	}
    }

#### 3.内置比较器 ####

import java.util.Map.Entry;
    import java.util.Set;
    import java.util.TreeMap;
    public class Test03 {
        
    
    	public static void main(String[] args) {
        
    		
    		TreeMap<Student,String> map = new TreeMap<>();
    		
    		map.put(new Student("孙尚香", '女', 22, "2211", "001"),"赏月");     
    		map.put(new Student("安吉拉", '女', 25, "2211", "002"),"闻香");     
    		map.put(new Student("虞姬", '女', 19, "2211", "003"),"听雨");     
    		map.put(new Student("妲己", '女', 29, "2211", "004"),"拾花");     
    		map.put(new Student("杨贵妃", '女', 21, "2211", "005"),"闻香");    
    		map.put(new Student("钟无艳", '女', 20, "2211", "006"),"听雨");    
    		map.put(new Student("貂蝉", '女', 19, "2211", "007"),"拾花");    
    		map.put(new Student("大桥", '女', 18, "2211", "008"),"赏月");    
    		map.put(new Student("伽罗", '女', 21, "2211", "009"),"赏花");    
    		map.put(new Student("黄忠", '男', 25, "2211", "010"),"酌酒");     
    		map.put(new Student("小乔", '女', 22, "2212", "001"),"赏花");    
    		map.put(new Student("阿珂", '女', 24, "2212", "002"),"闻香");    
    		map.put(new Student("瑶", '女', 20, "2212", "003"),"上身");   
    		map.put(new Student("上官婉儿", '女', 22, "2212", "004"),"酌酒");  
    		map.put(new Student("墨瞳茉拉", '女', 22, "2213", "004"),"抚琴"); 
    		
    		Set<Entry<Student, String>> entrySet = map.entrySet();
    		for (Entry<Student, String> entry : entrySet) {
        
    			System.out.println(entry);
    		}
    	}

public class Student implements Comparable<Student>{
        
    	
    	private String name;
    	private char sex;
    	private int age;
    	private String classId;
    	private String id;
    	
    	public Student() {
        
    	}
    	
    	public Student(String classId, String id) {
        
    		this.classId = classId;
    		this.id = id;
    	}
    
    	public Student(String name, char sex, int age, String classId, String id) {
        
    		this.name = name;
    		this.sex = sex;
    		this.age = age;
    		this.classId = classId;
    		this.id = id;
    	}
    
    	public String getName() {
        
    		return name;
    	}
    
    	public void setName(String name) {
        
    		this.name = name;
    	}
    
    	public char getSex() {
        
    		return sex;
    	}
    
    	public void setSex(char sex) {
        
    		this.sex = sex;
    	}
    
    	public int getAge() {
        
    		return age;
    	}
    
    	public void setAge(int age) {
        
    		this.age = age;
    	}
    
    	public String getClassId() {
        
    		return classId;
    	}
    
    	public void setClassId(String classId) {
        
    		this.classId = classId;
    	}
    
    	public String getId() {
        
    		return id;
    	}
    
    	public void setId(String id) {
        
    		this.id = id;
    	}
    	
    	//判断两个学生是否相同（班级号 + 学号）
    	@Override
    	public boolean equals(Object obj) {
        
    		if(this == obj){
        
    			return true;
    		}
    		
    		if(obj instanceof Student){
        
    			Student stu = (Student) obj;
    			if(classId.equals(stu.classId) && id.equals(stu.id)){
        
    				return true;
    			}
    		}
    		
    		return false;
    	}
    
    	@Override
    	public String toString() {
        
    		return name + "\t" + sex + "\t" + age + "\t" + classId + "\t" + id;
    	}
    
    	//排序规则：按照年龄排序
    	@Override
    	public int compareTo(Student o) {
        
    		//年龄差
    		int num = this.age - o.age;
    		if(num != 0){
        
    			return num;
    		}
    		
    		if(this == o || this.equals(o)){
        
    			return 0;
    		}
    		
    		return 1;//年龄相同，但是两个学生又不是同一个对象，我们还是返回1
    	}
    }

#### 4.外置比较器 ####

import java.util.Comparator;
    import java.util.Map.Entry;
    import java.util.Set;
    import java.util.TreeMap;
    
    public class Test04 {
        
    
    	public static void main(String[] args) {
        
    		
    		TreeMap<Student, String> map = new TreeMap<>(new Comparator<Student>() {
        
    
    			@Override
    			public int compare(Student o1, Student o2) {
        
    			if (o1 == o2 || o1.equals(o2)) {
        
    				return 0;
    			}
    			int len1 = o1.getName().length();
    			int len2 = o2.getName().length();
    			if (len1 != len2) {
        
    				return len1-len2;
    			}
    			int age1 = o1.getAge();
    			int age2 = o2.getAge();
    			if (age1 != age2) {
        
    				return age1-age2;
    			}
    				return 1;
    			}
    		});
    		map.put(new Student("孙尚香", '女', 22, "2211", "001"),"赏月");     
    		map.put(new Student("安吉拉", '女', 25, "2211", "002"),"闻香");     
    		map.put(new Student("虞姬", '女', 19, "2211", "003"),"听雨");     
    		map.put(new Student("妲己", '女', 29, "2211", "004"),"拾花");     
    		map.put(new Student("杨贵妃", '女', 21, "2211", "005"),"闻香");    
    		map.put(new Student("钟无艳", '女', 20, "2211", "006"),"听雨");    
    		map.put(new Student("貂蝉", '女', 19, "2211", "007"),"拾花");    
    		map.put(new Student("大桥", '女', 18, "2211", "008"),"赏月");    
    		map.put(new Student("伽罗", '女', 21, "2211", "009"),"赏花");    
    		map.put(new Student("黄忠", '男', 25, "2211", "010"),"酌酒");     
    		map.put(new Student("小乔", '女', 22, "2212", "001"),"赏花");    
    		map.put(new Student("阿珂", '女', 24, "2212", "002"),"闻香");    
    		map.put(new Student("瑶", '女', 20, "2212", "003"),"上身");   
    		map.put(new Student("上官婉儿", '女', 22, "2212", "004"),"酌酒");  
    		map.put(new Student("墨瞳茉拉", '女', 22, "2213", "004"),"抚琴");
    		
    		Set<Entry<Student,String>> entrySet = map.entrySet();
    		for (Entry<Student, String> entry : entrySet) {
        
    			System.out.println(entry);
    		}
    	}
    }

### 二、Sort ###

#### 1.ArrayList排序 ####

import java.util.ArrayList;
    import java.util.Comparator;
    
    public class Test01 {
        
    
    	public static void main(String[] args) {
        
    		
    		ArrayList<String> list = new ArrayList<>();
    		
    		list.add("d");
    		list.add("a");
    		list.add("bc");
    		list.add("b");
    		list.add("B");
    		list.add("bac");
    		list.add("e");
    		list.add("A");
    		list.add("ecz");
    		list.add("ea");
    		list.add("C");
    		list.add("c");
    		
    		list.sort(new Comparator<String>() {
        
    
    			@Override
    			public int compare(String o1, String o2) {
        
    				return o1.compareTo(o2);
    			}
    		});
    		
    		for (String element : list) {
        
    			System.out.println(element);
    		}
    	}
    }

#### 2.HashMap的value排序 ####

import java.util.ArrayList;
    import java.util.Comparator;
    import java.util.HashMap;
    import java.util.Map.Entry;
    import java.util.Set;
    
    public class Test02 {
        
    
    	public static void main(String[] args) {
        
    		
    		HashMap<String, Integer> map = new HashMap<>();
    		
    		 map.put("大桥",18);
    		 map.put("小乔",19);
    		 map.put("西施",25);
    		 map.put("王昭君",20);
    		 map.put("杨贵妃",23);
    		 map.put("貂蝉",28);
    		 
    			//将map所有的映射关系取出 -- entrySet()
    		 Set<Entry<String, Integer>> entrySet = map.entrySet();
    		 
    		//将Set集合转换为ArrayList集合
    		 ArrayList<Entry<String, Integer>> list = new ArrayList<>(entrySet);
    		 
    		 list.sort(new Comparator<Entry<String,Integer>>() {
        
    
    			@Override
    			public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
        
    				
    				Integer value1 = o1.getValue();
    				Integer value2 = o2.getValue();
    				if (value1 == value2) {
        
    					return 1;
    				}
    				return value1 - value2;
    			}
    		});
    		 for (Entry<String, Integer> entry : list) {
        
    			System.out.println(entry);
    		}
    	}
    }

### 三、Properties – 配置文件 ###

import java.io.IOException;
    import java.util.Properties;
    
    public class Test01 {
        
    	public static void main(String[] args) throws IOException {
        
    		
    		//创建配置文件对象
    		Properties properties = new Properties();
    		
    		//将配置文件加载到对象中
    		properties.load(Test01.class.getClassLoader().getResourceAsStream("DBConfig.properties"));
    		
    		//读取配置文件中的数据
    		String username = properties.getProperty("username");
    		String password = properties.getProperty("password");
    		System.out.println(username + " -- " + password);
    		
    	}
    }

>     username=gl
>     password=123456

### 四、Collections – 集合工具类 ###

import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.Collections;
    import java.util.Comparator;
    
    public class Test01 {
        
    
    	public static void main(String[] args) {
        
    		
    		ArrayList<String> list = new ArrayList<>();
    		
    		//批量添加
    		Collections.addAll(list, "c","a","d","b");
    		
    		//使用集合中元素的内置比较器进行排序
    		Collections.sort(list);
    		
    		//使用外置置比较器进行排序
    		Collections.sort(list, new Comparator<String>() {
        
    
    			@Override
    			public int compare(String o1, String o2) {
        
    				return -o1.compareTo(o2);
    			}
    		});
    		
    		//替换
    		Collections.fill(list, "abc");
    		
    		System.out.println(Arrays.toString(list.toArray()));
    	}
    }

### 五、总结 ###

#### 1.Collection 与 Map的区别 ####

##### 1.Collection 存单个值，可以获取迭代器进行遍历 #####

##### 2.Map存两个值(Key-Value)，不可以获取迭代器，不能遍历（Map可以间接遍历） #####

#### 2.ArrayList 与 LinkedList的区别 ####

##### 1.使用上的区别： #####

> ##### LinkedList添加了 #####
> 
> ##### 队列模式-先进先出（removeFirst（）） #####
> 
> ##### 栈模式-先进后出（removeLast（）） #####

##### 2.效率上的区别： #####

###### 1.ArrayList底层数据结构是一维数组 ######

###### 2.LinkedList底层数据结构是双向链表 ######

> ##### 添加 - 不扩容的情况：ArrayList快 #####
> 
> ##### 添加 - 扩容的情况：LinkedList快 #####
> 
> ##### 删除：LinkedList快 #####
> 
> ##### 查询：ArrayList快 #####
> 
> ##### 修改：ArrayList快 #####

###### 3.注意：工作中常用ArrayList，因为很多需求都需要使用查询功能，ArrayList查询更快 ######

#### 3.各种集合的应用场景 ####

##### 1.ArrayList：存数据，线程不安全 #####

##### 2.LinkedLinked：队列模式、栈模式，线程不安全 #####

##### 3.Vector：弃用，线程安全 #####

##### 4.Stack：弃用，线程安全 #####

##### 5.HashSet：去重+无序，线程不安全 #####

##### 6.LinkedHashSet：去重+有序，线程不安全 #####

##### 7.TreeSet：排序，线程不安全 #####

##### 8.HashMap：存key+value，key去重，无序，线程不安全 #####

##### 9.LinkedHashMap：存key+value，key去重，有序，线程不安全 #####

##### 10.Hashtable：弃用，存key+value，key去重，无序，线程安全，方法加锁-效率低 #####