java-基础知识

finalize 是一个方法名，在垃圾回收器将对象从内存中清除出去之前做一些必要的清理工作

实现Runnable接口比继承Thread类所具有的优势：

1）：适合多个相同的程序代码的线程去处理同一个资源

2）：可以避免java中的单继承的限制

3）：增加程序的健壮性，代码可以被多个线程共享，代码和数据独立

String类length（）方法字符串长度，数组的length属性数组大小，

string的实现采用了Flyweight享元设计模式

 

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 == 47)
            System.out.println("Created 47");
    }
    protected void finalize() {
        if(!gcrun) {
            gcrun = true;
            System.out.println("Beginning to finalize after " + created + " Chairs have been created");
        }
        if(i == 47) {
            System.out.println("Finalizing Chair #47， " +"Setting flag to stop Chair creation");
            f = true;
        }
        finalized++;
        if(finalized >= created)
            System.out.println("All " + finalized + " finalized");
    }
}

public class HelloAgent {
    public static void main(String[] args) {
        if(args.length == 0) {
            System.err.println("Usage: /n" + "<a href=\"http://lib.youkuaiyun.com/base/java\" class='replace_word' title=\"Java 知识库\" target='_blank' style='color:#df3434; font-weight:bold;'>Java </a>Garbage before/n or:/n" + "java Garbage after");
            return;
        }
        while(!Chair.f) {
            new Chair();
            new String("To take up space");
        }
        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();
        }
        System.out.println("bye!");
        if(args[0].equals("after"))
            System.runFinalizersOnExit(true);
    }
}


class MyThread2 extends Thread{

    @Override
    public void run() {
        System.out.println("Thread will throws exception");
        throw new RuntimeException("myown exception from thread");
    }
}
public class HelloAgent{

    public static void main(String[] args){
        Thread.UncaughtExceptionHandler handler = new Thread.UncaughtExceptionHandler(){

            @Override
            public void uncaughtException(Thread t, Throwable e) {
                System.out.println("Uncaught excepiton"+e);
            }
        };
        Thread myThread=new MyThread2();
        myThread.setUncaughtExceptionHandler(handler);
        myThread.start();
    }
}