内存泄漏实例, 深层次认识list对象在内存中使用

import java.util.ArrayList;
import java.util.List;

public class JavaMemory2
{
private List list = new ArrayList();

static float freeMem = 0f;
static float totalMem = 0f;
static float maxMem = 0f;
static float usedMemRate = 0f;

static
{
System.out.println("-----------系统初始时内存情况---------------");
showMem();
}

public static void showMem()
{
freeMem = Runtime.getRuntime().freeMemory()/1024/1024; 
totalMem = Runtime.getRuntime().totalMemory()/1024/1024; 
maxMem = Runtime.getRuntime().maxMemory()/1024/1024;
usedMemRate = (totalMem - freeMem) / maxMem * 100.0f;

        StringBuilder sb = new StringBuilder();  
        sb.append("最大内存:" + maxMem + " MB\n")  
          .append("当前最大内存:" + totalMem + " MB\n")  
          .append("当前空闲内存:" + freeMem + " MB\n")
          .append("当前已使用的内存:" + (totalMem - freeMem) + " MB\n")
          .append("实际jvm剩余内存:" + (maxMem - (totalMem - freeMem)) );
        System.out.println(sb.toString());
}

public void f()
{
B b1 = new B();
list.add(b1);
System.out.println("--------------------");
showMem();
}

public void f2()
{
List al = list;
// list = null;   //此时并没有回收堆中内存b1, 因为还存在引用
// list.clear();  //可以回收内存b1
B b2 = new B();
al.add(b2);

System.out.println("--------------------");
showMem();

B b3 = new B();
al.add(b3);
}

public static void main(String[] args)
{
JavaMemory2 jmp = new JavaMemory2();
jmp.f();
jmp.f2();
}
}

class B
{
public byte[] data1 = new byte[(int)(Runtime.getRuntime().maxMemory() * 0.4)];
public int b;
}