Map接口

野性酷女 2022-05-17 13:11 227阅读 0赞

public class Customer {
    	private String name;
    	private Integer id;
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	public Integer getId() {
    		return id;
    	}
    	public void setId(Integer id) {
    		this.id = id;
    	}
    	public Customer(String name, Integer id) {
    		super();
    		this.name = name;
    		this.id = id;
    	}
    	public Customer() {
    		super();
    	}
    	@Override
    	public String toString() {
    		return "Customer [name=" + name + ", id=" + id + "]";
    	}
    	@Override
    	public int hashCode() {
    		final int prime = 31;
    		int result = 1;
    		result = prime * result + ((id == null) ? 0 : id.hashCode());
    		result = prime * result + ((name == null) ? 0 : name.hashCode());
    		return result;
    	}
    	@Override
    	public boolean equals(Object obj) {
    		if (this == obj)
    			return true;
    		if (obj == null)
    			return false;
    		if (getClass() != obj.getClass())
    			return false;
    		Customer other = (Customer) obj;
    		if (id == null) {
    			if (other.id != null)
    				return false;
    		} else if (!id.equals(other.id))
    			return false;
    		if (name == null) {
    			if (other.name != null)
    				return false;
    		} else if (!name.equals(other.name))
    			return false;
    		return true;
    	}
    	
    }

public class Person {
    	private String name;
    	private Integer age;
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	public Integer getAge() {
    		return age;
    	}
    	public void setAge(Integer age) {
    		this.age = age;
    	}
    	protected Person(String name, Integer age) {
    		super();
    		this.name = name;
    		this.age = age;
    	}
    	@Override
    	public String toString() {
    		return "Person [name=" + name + ", age=" + age + "]";
    	}
    	@Override
    	public boolean equals(Object obj) {
    		if (this == obj)
    			return true;
    		if (obj == null)
    			return false;
    		if (getClass() != obj.getClass())
    			return false;
    		Person other = (Person) obj;
    		if (age == null) {
    			if (other.age != null)
    				return false;
    		} else if (!age.equals(other.age))
    			return false;
    		if (name == null) {
    			if (other.name != null)
    				return false;
    		} else if (!name.equals(other.name))
    			return false;
    		return true;
    	}
    	
    }

import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.util.Collection;
    import java.util.Comparator;
    import java.util.HashMap;
    import java.util.Iterator;
    import java.util.LinkedHashMap;
    import java.util.Map;
    import java.util.Properties;
    import java.util.Set;
    import java.util.TreeMap;
    
    import org.junit.Test;
    
    /*
     * Collection接口
     * 
     * Map接口
     * 		|-----HashMap:Map的主要实现类
     * 		|-----LinkedHashMap:使用链表维护添加进Map中的顺序。故遍历Map时，是按添加的顺序遍历的。
     * 		|-----TreeMap:按照添加进Map中的元素的key的指定属性进行排序。要求：key必须是同一个类的对象！
     * 				针对key：自然排序   vs 定制排序
     * 		|-----Hashtable:古老的实现类，线程安全，不建议使用。
     * 			|----Properties:常用来处理属性文件。键和值都为String类型的
     */
    public class TestMap {
    	//使用Properties处理属性文件
    	@Test
    	public void test6() throws FileNotFoundException, IOException{
    		Properties pros = new Properties();
    		pros.load(new FileInputStream(new File("jdbc.properties")));
    		String user = pros.getProperty("user");
    		System.out.println(user);
    		String password = pros.getProperty("password");
    		System.out.println(password);
    	}
    	
    	// 定制排序
    	@Test
    	public void test5() {
    		Comparator com = new Comparator() {
    			public int compare(Object o1, Object o2) {
    				if (o1 instanceof Customer && o2 instanceof Customer) {
    					Customer c1 = (Customer) o1;
    					Customer c2 = (Customer) o2;
    					int i = c1.getId().compareTo(c2.getId());
    					if (i == 0) {
    						return c1.getName().compareTo(c2.getName());
    					}
    					return i;
    				}
    				return 0;
    			}
    		};
    		TreeMap map = new TreeMap(com);
    		map.put(new Customer("AA", 1001), 87);
    		map.put(new Customer("CC", 1001), 67);
    		map.put(new Customer("MM", 1004), 77);
    		map.put(new Customer("GG", 1002), 97);
    		
    		Set set1 = map.keySet();
    		for (Object obj : set1) {
    			System.out.println(obj + "----->" + map.get(obj));
    		}
    	}
    
    	// 自然排序
    	@Test
    	public void test4() {
    		Map map = new TreeMap();
    		map.put(new Person("AA", 23), 89);
    		map.put(new Person("MM", 22), 79);
    		map.put(new Person("GG", 23), 99);
    		map.put(new Person("JJ", 13), 69);
    
    		Set set1 = map.keySet();
    		for (Object obj : set1) {
    			System.out.println(obj + "----->" + map.get(obj));
    		}
    	}
    
    	@Test
    	public void test3() {
    		Map map = new LinkedHashMap();
    		map.put("AA", 213);
    		map.put("BB", 45);
    		map.put(123, "CC");
    		map.put(null, null);
    		map.put(new Person("DD", 23), 89);
    
    		Set set1 = map.keySet();
    		for (Object obj : set1) {
    			System.out.println(obj + "----->" + map.get(obj));
    		}
    	}
    
    	/*
    	 * 如何遍历Map Set keySet() Collection values() Set entrySet()
    	 */
    	@Test
    	public void test2() {
    		Map map = new HashMap();
    		map.put("AA", 213);
    		map.put("BB", 45);
    		map.put(123, "CC");
    		map.put(null, null);
    		map.put(new Person("DD", 23), 89);
    
    		// 1.遍历key集。
    		Set set = map.keySet();
    		for (Object obj : set) {
    			System.out.println(obj);
    		}
    		// 2.遍历value集
    		Collection values = map.values();
    		Iterator i = values.iterator();
    		while (i.hasNext()) {
    			System.out.println(i.next());
    		}
    		// 3.如何遍历key-value对。
    		// 方式一：
    		Set set1 = map.keySet();
    		for (Object obj : set1) {
    			System.out.println(obj + "----->" + map.get(obj));
    		}
    		// 方式二：
    		Set set2 = map.entrySet();
    		for (Object obj : set2) {
    			Map.Entry entry = (Map.Entry) obj;
    			// System.out.println(entry.getKey() + "---->" + entry.getValue());
    			System.out.println(entry);
    		}
    	}
    
    	/*
    	 * Object put(Object key,Object value):向Map中添加一个元素 Object remove(Object
    	 * key):按照指定的key删除此key-value void putAll(Map t) void clear():清空 Object
    	 * get(Object key)：获取指定key的value值。若无此key，则返回null boolean containsKey(Object
    	 * key) boolean containsValue(Object value) int size():返回集合的长度 boolean
    	 * isEmpty() boolean equals(Object obj)
    	 * 
    	 * HashMap： 1.key是用Set来存放的，不可重复。value是用Collection来存放的，可重复
    	 * 一个key-value对，是一个Entry。所有的Entry是用Set存放的，也是不可重复的。
    	 * 2.向HashMap中添加元素时，会调用key所在类的equals()方法，判断两个key是否相同。若相同 则只能添加进后添加的那个元素。
    	 */
    	
    	
    	@Test
    	public void test1() {
    		Map map = new HashMap();
    		map.put("AA", 213);
    		map.put("BB", 456);
    		map.put("BB", 45);
    		map.put(123, "CC");
    		map.put(null, null);
    		map.put(new Person("DD", 23), 89);
    		map.put(new Person("DD", 23), 87);
    		System.out.println(map.size());
    		System.out.println(map);
    		map.remove("BB");
    		System.out.println(map);
    		Object value = map.get(1234);
    		System.out.println(value);
    	}
    }