package selfimpr.ThinkInJava.gc;

public class Chair {
    static boolean gcrun = false;
    static boolean f = false;
    static int created = 0;
    static int finalized = 0;
    int i;
    Chair() {
        i = ++created;
        if(created == 35000)
            System.out.println("Created 35000");
    }
    protected void finalize() {
        //检测gc的第一次运行,gc第一次运行时调用finalize方法会触发并输出
        if(!gcrun) {
            gcrun = true;
            System.out.println("Beginning to finalize after " +
                    created + " Chairs have been ced. ");
        }
        //监测收集编号i值为35000的Chair对象.
        if(i==35000) {
            System.out.println("Finalizing Chair #35000, " + "i" + i + " " + created +
                    "Setting flag to stop Chair creation");
            //当i值为35000的Chair的对象被垃圾收集后, 将f设置为true, 结束创建.
            f = true;
        }
        //记录销毁对象的数目
        finalized ++;
        if(finalized >= created-100) 
            System.out.println("All " + finalized + " finalized");
    }
}

package selfimpr.ThinkInJava.gc;

public class Garbage {

    public static void main(String[] args) {
        if(args.length == 0) {
            System.err.println("Usage: \n" +
                    "java Garbage before\n or:\n" +
                    "java Garbage after");
            return ;
        }
        //1. Chair.f为假时不断的创建Chair和String对象.
        while(!Chair.f) {
            new Chair();
            new String("To take up space");
        }
        //结束创建活动后, 打印总共被创建了多少Chair对象.
        //在这个过程中, JVM自动运行的垃圾回收回收了多少个Chair对象.
        System.out.println("After all Chairs have been created:\n" +
                "total created = " + Chair.created + 
                ", total finalized = " + Chair.finalized);
        if(args[0].equals("before")) {
            System.out.println("gc():");
            System.gc();
            System.out.println("runFinalization():");
            System.runFinalization();
        }
        //这个地方进行了改动, 下面这两行代码是新加的.
        //这里我做了两次测试
        /*
         * 第一次, 调用一次System.gc();
         * 第二次, 调用两次System.gc();
         * 然而, 和Think in java的讲法不同, 我调用第一System.gc()的时候, 
         * 程序中没有释放的其他对象的finalize方法并没有被调用.
         * 而我调用两次System.gc();所有没有被释放的对象的finalize方法都被调用了.
         * 
         * 因此, 感觉至少在jdk6.0_update_10中, GC的运行是在第二次的时候,
         * 才调用finalize方法并释放内存的.
         */
        System.gc();
        System.gc();
        
        //被改动的代码结束
        
        System.out.println("bye!");
        if(args[0].equals("after"))
            System.runFinalizersOnExit(true);
    }

}