public class StrongReferenceTest { public static int M = 1024*1024; public static void printlnMemory(String tag){ Runtime runtime = Runtime.getRuntime(); int M = StrongReferenceTest.M; System.out.println("\n"+tag+":"); System.out.println(runtime.freeMemory()/M+"M(free)/" + runtime.totalMemory()/M+"M(total)"); } public static void main(String[] args){ StrongReferenceTest.printlnMemory("1.原可用内存和总内存"); //实例化10M的数组并与strongReference建立强引用 byte[] strongReference = new byte[10*StrongReferenceTest.M]; StrongReferenceTest.printlnMemory("2.实例化10M的数组,并建立强引用"); System.out.println("strongReference : "+strongReference); System.gc(); StrongReferenceTest.printlnMemory("3.GC后"); System.out.println("strongReference : "+strongReference); //strongReference = null;后,强引用断开了 strongReference = null; StrongReferenceTest.printlnMemory("4.强引用断开后"); System.out.println("strongReference : "+strongReference); System.gc(); StrongReferenceTest.printlnMemory("5.GC后"); System.out.println("strongReference : "+strongReference); }}
运行结果:
2.弱引用 WeakReference
如果一个对象只具有弱引用,无论内存充足与否,Java GC后对象如果只有弱引用将会被自动回收。
public class WeakReferenceTest { public static int M = 1024*1024; public static void printlnMemory(String tag){ Runtime runtime = Runtime.getRuntime(); int M = WeakReferenceTest.M; System.out.println("\n"+tag+":"); System.out.println(runtime.freeMemory()/M+"M(free)/" + runtime.totalMemory()/M+"M(total)"); } public static void main(String[] args){ WeakReferenceTest.printlnMemory("1.原可用内存和总内存"); //创建弱引用 WeakReference