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）

 import java.util.HashMap;

 import java.util.Map;

 public class MemoryLeak {

  public static void main(String[] args) {

   Map<Key, String> map = new HashMap<Key, String>(1000);

   int counter = 0;

   while (true) {

        // creates duplicate objects due to bad Key class

    map.put(new Key("dummyKey"), "value");

    counter++;

    if (counter % 1000 == 0) {

     System.out.println("map size: " + map.size());

     System.out.println("Free memory after count " + counter

       + " is " + getFreeMemory() + "MB");

     sleep(1000);

    }

   }

  }

  // inner class key without hashcode() or equals() -- bad implementation

  static class Key {

   private String key;

   public Key(String key) {

    this.key = key;

   }

  }

  //delay for a given period in milli seconds

  public static void sleep(long sleepFor) {

   try {

    Thread.sleep(sleepFor);

   } catch (InterruptedException e) {

    e.printStackTrace();

   }

  }

  //get available memory in MB

  public static long getFreeMemory() {

   return Runtime.getRuntime().freeMemory() / (1024 * 1024);

  }

 }