java内存问题排查及分析

最近了解了一下jdk对于jvm分析工具的使用，下面通过一个简单的列子介绍一下，以下内容部分来自其他帖子。

下面这段代码明显有问题（从网上抄的）

 1 import java.util.HashMap;
 2 import java.util.Map;
 3 
 4 public class MemoryLeak {
 5 
 6  public static void main(String[] args) {
 7   Map<Key, String> map = new HashMap<Key, String>(1000);
 8 
 9   int counter = 0;
10   while (true) {
11        // creates duplicate objects due to bad Key class
12    map.put(new Key("dummyKey"), "value");
13    counter++;
14    if (counter % 1000 == 0) {
15     System.out.println("map size: " + map.size());
16     System.out.println("Free memory after count " + counter
17       + " is " + getFreeMemory() + "MB");
18 
19     sleep(1000);
20    }
21 
22     
23   }
24  }
25 
26  // inner class key without hashcode() or equals() -- bad implementation
27  static class Key {
28   private String key;
29 
30   public Key(String key) {
31    this.key = key;
32   }
33 
34  }
35 
36  //delay for a given period in milli seconds
37  public static void sleep(long sleepFor) {
38   try {
39    Thread.sleep(sleepFor);
40   } catch (InterruptedException e) {
41    e.printStackTrace();
42   }
43  }
44 
45  //get available memory in MB
46  public static long getFreeMemory() {
47   return Runtime.getRuntime().freeMemory() / (1024 * 1024);
48  }
49 
50 }