简单看了一下java的几种引用类型,先贴着,有时间来整理.

import java.lang.ref.SoftReference;

import java.lang.ref.WeakReference;

public class ReferenceTest {

public static void main(String[] args) throws Throwable {

//strong();

soft();

//weak();

}

/**

* 强引用

* (最常见的引用,如果一个对象具有强引用, VM宁愿抛出 OutOfMemoryError 都不会回收它)

*/

public static void strong(){

System.out.println("MAX Mem\t:" + (Runtime.getRuntime().maxMemory()/1024/1024));

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

String[] strs = new String[9999999]; //存放String数组对象的强引用

System.out.println("=======================");

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

String[] strs1 = new String[9999999]; //存放String数组对象的强引用

}

/**

* 软引用

* (不保证对象一定会被回收:不管是否显式gc,内存不足时才会回收)

*/

public static void soft(){

System.out.println("MAX Mem\t:" + (Runtime.getRuntime().maxMemory()/1024/1024));

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

String[] strs = new String[9999999]; //存放String对象的强引用

System.out.println("=======================");

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

SoftReference sr = new SoftReference(strs);//一个软引用指向strs

strs = null;//释放strs的强引用

System.out.println(sr.get());//回收以后通过软引用访问strs(没有被回收)

System.gc();

System.out.println(sr.get());//回收以后通过软引用访问strs(没有被回收)

System.out.println("=======================");

String[] strs1 = new String[9999999]; //存放String对象的强引用

System.out.println(sr.get());//回收以后通过软引用访问strs(已经被回收)

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

}

/**

* 弱引用

* (对象一定会被回收:调用gc后马上回收)

*/

public static void weak(){

System.out.println("MAX Mem\t:" + (Runtime.getRuntime().maxMemory()/1024/1024));

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

String[] strs = new String[9999999]; //存放String对象的强引用

System.out.println("=======================");

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

WeakReference sr = new WeakReference(strs);//一个弱引用指向strs

strs = null;//释放strs的强引用

System.out.println("GC前: \t" + sr.get());//回收以后通过弱引用访问strs(GC前没有被回收)

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

System.gc();

System.out.println("GC后: \t" + sr.get());//回收以后通过弱引用访问strs(GC后已经被回收)

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

System.out.println("=======================");

String[] strs1 = new String[9999999]; //存放String对象的强引用

System.out.println("GC后: \t" + sr.get());//回收以后通过弱引用访问strs(GC后已经被回收)

System.out.println("FREE Mem\t:" + (Runtime.getRuntime().freeMemory()/1024/1024));

}

}