tests/gc/ClassUnload.java

   1 import java.util.Vector;
   2 import java.io.FileInputStream;
   3
   4 class ClassUnloadTest {
   5         public static Vector classEater;
   6
   7         public static void classTest() {
   8                 System.out.println("TC: Testclass eats up memory ...");
   9                 classEater = new Vector();
  10                 for (int i=0; i<1000000; i++)
  11                         classEater.add(new String("I am a memory eater!"));
  12
  13                 System.out.println("TC: Testclass fine.");
  14         }
  15
  16         static {
  17                 System.out.println("TC: Static Initializer ...");
  18         }
  19 }
  20
  21 class ClassUnloadLoader extends ClassLoader {
  22         public Vector myEater;
  23
  24         public ClassUnloadLoader() {
  25                 super();
  26                 System.out.println("CL: Initializer ...");
  27         }
  28
  29         public Class myLoad() {
  30                 Class c;
  31
  32                 System.out.println("CL: Classloader loads testing class ...");
  33                 try {
  34                         c = loadClass("ClassUnloadTest");
  35                         ClassUnloadTest.classTest();
  36                 } catch (Exception e) {
  37                         System.out.println("EXCEPTION: " + e);
  38                         c = null;
  39                 }
  40
  41                 System.out.println("CL: Classloader eats up memory ...");
  42                 myEater = new Vector();
  43                 for (int i=0; i<1000000; i++)
  44                         myEater.add(new String("I am a memory eater!"));
  45
  46                 return c;
  47         }
  48
  49         public Class loadClass(String name) throws ClassNotFoundException {
  50                 Class c;
  51                 FileInputStream s;
  52                 byte[] buf;
  53                 int size;
  54
  55                 if (name != "ClassUnloadTest") {
  56                         c = super.loadClass(name);
  57                         return c;
  58                 }
  59
  60                 System.out.println("CL: Now loading \'" + name + "\' ...");
  61                 try {
  62                         s = new FileInputStream(name + ".class");
  63                         size = s.available();
  64                         buf = new byte[size];
  65                         s.read(buf);
  66                         System.out.println("\tloaded a total of " + size + " bytes.");
  67                         c = super.defineClass(name, buf, 0, size);
  68                 } catch (Exception e) {
  69                         System.out.println("EXCEPTION: " + e);
  70                         throw new ClassNotFoundException();
  71                 }
  72
  73                 return c;
  74         }
  75
  76         protected void finalize() {
  77                 System.out.println("CL: Classloader will be unloaded ...");
  78         }
  79 }
  80
  81 public class ClassUnload {
  82         public static void printMemInfo() {
  83                 Runtime r = Runtime.getRuntime();
  84                 /*System.out.println("\tfree : " + r.freeMemory());*/
  85                 /*System.out.println("\ttotal: " + r.totalMemory());*/
  86                 /*System.out.println("\tmax  : " + r.maxMemory());*/
  87                 System.out.println("\tused : " + (r.totalMemory() - r.freeMemory()));
  88         }
  89
  90         public static void main(String[] s) {
  91                 ClassUnloadLoader l;
  92                 Class c;
  93
  94                 System.out.println("--: Running program ...");
  95                 printMemInfo();
  96
  97                 System.out.println("--: Create classloader ...");
  98                 l = new ClassUnloadLoader();
  99
 100                 System.out.println("--: Load stuff ...");
 101                 c = l.myLoad();
 102                 System.out.println("\tclass = " + c);
 103
 104                 printMemInfo();
 105
 106                 /*System.out.println("\tDEBUG l=" + l);*/
 107                 /*System.out.println("\tDEBUG c=" + c);*/
 108                 /*System.out.println("\tDEBUG c.loader=" + c.getClassLoader());*/
 109
 110                 /* REMEMBER: if you comment out one of the following two lines, no class unloading should happen! */
 111                 l = null;
 112                 c = null;
 113
 114                 System.out.println("--: Collect stuff ...");
 115                 System.gc();
 116                 System.gc();
 117                 System.gc();
 118
 119                 printMemInfo();
 120
 121                 /*System.out.println("\tDEBUG l=" + l);*/
 122                 /*System.out.println("\tDEBUG c=" + c);*/
 123                 /*System.out.println("\tDEBUG c.loader=" + (c==null ? null : c.getClassLoader()));*/
 124
 125                 System.out.println("done.");
 126         }
 127 }