Java中TreeMap VS HashMap_JAVA_编程开发_程序员俱乐部

class="p0">Key是长度为11的String,?Value是Short。

HashMap使用default?load?factor?(0.75).

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Size为100000：

TreeMap?占用了8.91M内存；search?100000?times,?usedTime:?268ms.

HashMap占用了9.65M内存；search?100000?times,?usedTime:?54ms.

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Size为1000000：

TreeMap?占用了91.5M内存；search?100000?times,?usedTime:?636ms.

HashMap占用了95.88M内存；search?100000?times,?usedTime:?83ms.

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在数据量为十万到百万之间时，HashMap占用的内存比TreeMap多了5%-8%，查询时间只有TreeMap的13%-20%，因此在这一应用场景下，HashMap是较好的选择。

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测试代码如下：

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import java.util.HashMap;
import java.util.Random;
import java.util.TreeMap;


public class TreeMapVSHashMap {
	private static Random random = new Random();
	private static Random random2 = new Random();
	
	private static final int SIZE = 100000;
	private static final int GETCNT = 100000;

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
		TreeMapTest();		
		
//		HashMapTest();
		

	}
	
	public static void TreeMapTest() {
		System.out.println("\nTreeMap Test");
		System.gc();
		printHeapMemoryInfo();
		TreeMap<String, Short> trMap = new TreeMap<String, Short>();
		int i = 0;
		Short val;
		while (i < SIZE) {
			val = trMap.put(getRandomPhone(), (short)(i%4));
			
			if (val == null) {
				i++;
			}
		}
		
		System.out.println("size : " + trMap.size());
			
		System.gc();
		printHeapMemoryInfo();
		
		long startTime = System.currentTimeMillis();
		for (i=0; i<GETCNT; i++) {
			trMap.get(getRandomPhone2());
		}
		System.out.println("search " + GETCNT + " times, usedTime: " + (System.currentTimeMillis() - startTime) + "ms.");
		
	}
	
	public static void HashMapTest() {
		System.out.println("\nHashMap Test");
		System.gc();
		printHeapMemoryInfo();
		HashMap<String, Short> hashMap = new HashMap<String, Short>();
		int i = 0;
		Short val;
		while (i < SIZE) {
			val = hashMap.put(getRandomPhone(), (short)(i%4));
			
			if (val == null) {
				i++;
			}
		}
		
		System.out.println("size : " + hashMap.size());
		
		System.gc();
		printHeapMemoryInfo();
		
		long startTime = System.currentTimeMillis();
		for (i=0; i<GETCNT; i++) {
			hashMap.get(getRandomPhone2());
		}
		System.out.println("search " + GETCNT + " times, usedTime: " + (System.currentTimeMillis() - startTime) + "ms.");

	}

	/**
	 * 返回一个手机号码，有十亿种可能性，（中国移动用户总数约十亿）
	 * @return
	 */
	public static String getRandomPhone() {
		return String.valueOf(13000000000L + random.nextInt(1000000000));
	}
	
	/**
	 * 返回一个测试手机号码，有十亿种可能性，（中国移动用户总数约十亿）
	 * @return
	 */
	public static String getRandomPhone2() {
		return String.valueOf(13000000000L + random2.nextInt(1000000000));
	}


	public static void printHeapMemoryInfo() {
		Runtime runtime = Runtime.getRuntime();
		System.out.printf("maxMemory : %.2fM\n", runtime.maxMemory()*1.0/1024/1024);
		System.out.printf("totalMemory : %.2fM\n", runtime.totalMemory()*1.0/1024/1024);
		System.out.printf("freeMemory : %.2fM\n", runtime.freeMemory()*1.0/1024/1024);
		System.out.printf("usedMemory : %.2fM\n", (runtime.totalMemory()-runtime.freeMemory())*1.0/1024/1024);
	}
}

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