TreeMap 实现类

可以对 key 进行排序，但必须要集合元素必须实现 Comparable 接口或者接口必须实现 Comparator 比较器

常用方法

两种实现方式

元素实现 Comparable 接口

package 集合;

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class TreeMapDemo implements Comparable {
	private String name;
	private int 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;
	}

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

	@Override
	public String toString() {
		return "[name=" + name + ", age=" + age + "]";
	}

	//比较规则：先比较名字再比较年龄
	@Override
	public int compareTo(Object o) {
		TreeMapDemo t = (TreeMapDemo) o;
		int n1 = this.getName().compareTo(t.getName());
		int n2 = this.getAge() - t.getAge();
		return n1 == 0 ? n2 : n1;
	}
	public static void main(String[] args) {
		TreeMap<TreeMapDemo, String> tree = new TreeMap<>();
		TreeMapDemo t1 = new TreeMapDemo("a张三", 21);
		TreeMapDemo t2 = new TreeMapDemo("c李四", 22);
		TreeMapDemo t3 = new TreeMapDemo("b王五", 19);
		tree.put(t1, "北京");
		tree.put(t2, "上海");
		tree.put(t3, "杭州");
		System.out.println(tree.size());
		System.out.println(tree);
		//添加名字相同年龄不同的key后
		TreeMapDemo t4 = new TreeMapDemo("b王五", 17);
		tree.put(t4, "武汉");
		System.out.println(tree.size());
		System.out.println(tree);
		//添加相同的key，覆盖
		tree.put(t4, "深圳");
		System.out.println(tree.size());
		System.out.println(tree);
		//两种遍历方式
		System.out.println("------keyset遍历--------");
		Set<TreeMapDemo> key = tree.keySet();
		Iterator<TreeMapDemo> it = key.iterator();
		 while(it.hasNext()) {
			 TreeMapDemo s = it.next();
			 System.out.println(s + "=" + tree.get(s));
		 }
		 System.out.println("-------entry遍历--------------");
		 Set<Map.Entry<TreeMapDemo, String>> entries = tree.entrySet();
		 for (Map.Entry<TreeMapDemo, String> entry : entries) {
			System.out.println(entry);
		}
	}
}
/*
3
{[name=a张三, age=21]=北京, [name=b王五, age=19]=杭州, [name=c李四, age=22]=上海}
4
{[name=a张三, age=21]=北京, [name=b王五, age=17]=武汉, [name=b王五, age=19]=杭州, [name=c李四, age=22]=上海}
4
{[name=a张三, age=21]=北京, [name=b王五, age=17]=深圳, [name=b王五, age=19]=杭州, [name=c李四, age=22]=上海}
------keyset遍历--------
[name=a张三, age=21]=北京
[name=b王五, age=17]=深圳
[name=b王五, age=19]=杭州
[name=c李四, age=22]=上海
-------entry遍历--------------
[name=a张三, age=21]=北京
[name=b王五, age=17]=深圳
[name=b王五, age=19]=杭州
[name=c李四, age=22]=上海

*/

使用比较器

package 集合;

import java.util.Comparator;
import java.util.TreeMap;

public class TreeMap2 {
	private String name;
	private int 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;
	}
	public TreeMap2(String name, int age) {
		super();
		this.name = name;
		this.age = age;
	}
	@Override
	public String toString() {
		return "[name=" + name + ", age=" + age + "]";
	}
	public static void main(String[] args) {
		TreeMap<TreeMap2, String> tree = new TreeMap<TreeMap2, String>(new Comparator<TreeMap2>() {
			//比较规则，先比较名字长短，再比较年龄
			@Override
			public int compare(TreeMap2 o1, TreeMap2 o2) {
				int n1 = o1.name.length() - o2.name.length();
				int n2 = o1.age - o2.age;
				return n1 == 0 ? n2 : n1;
			}
		});
		TreeMap2 t1 = new TreeMap2("Bob", 21);
		TreeMap2 t2 = new TreeMap2("Ernest", 20);
		TreeMap2 t3 = new TreeMap2("Frank",19);
		tree.put(t1, "伦敦");
		tree.put(t2, "纽约");
		tree.put(t3, "华盛顿");
		System.out.println(tree.size());
		System.out.println(tree);
		//添加名字长短一样，年龄不同的key后
		TreeMap2 t4 = new TreeMap2("Abc", 19);
		tree.put(t4, "旧金山");
		System.out.println(tree.size());
		System.out.println(tree);
		//添加相同的键，将覆盖值
		tree.put(t4, "悉尼");
		System.out.println(tree.size());
		System.out.println(tree);
	}
}
/*
3
{[name=Bob, age=21]=伦敦, [name=Frank, age=19]=华盛顿, [name=Ernest, age=20]=纽约}
4
{[name=Abc, age=19]=旧金山, [name=Bob, age=21]=伦敦, [name=Frank, age=19]=华盛顿, [name=Ernest, age=20]=纽约}
4
{[name=Abc, age=19]=悉尼, [name=Bob, age=21]=伦敦, [name=Frank, age=19]=华盛顿, [name=Ernest, age=20]=纽约}
*/

标签：返回,name,映射,实现,age,tree,TreeMap,key
来源： https://blog.csdn.net/m0_52423355/article/details/122653695