Try finally的一个实验和为什么避免重载 finalize()方法--例子

public class TryFinallTest {

public TryFinallTest(){

}
public void runSomething(String str){
System.out.println(str);
}

public static void typeOne(){

TryFinallTest one = new TryFinallTest();
try{
one.runSomething("runing something");
return;
}finally{
one.runSomething("do final work");
}
}
public static void main(String[] args){

TryFinallTest.typeOne();
}
}

输出结果:

runing something

do final work

也就是，只要存在try finally,那么，finally包围的语句块一定会执行。

 

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<<effectiva Java>>中提到，避免使用finalize方法来执行资源清理工作，避免使用finallize方法。

那么，为什么？

例子１:

public class TryCatchFinallyTest implements Runnable {

private void testMethod() throws InterruptedException {
try {
System.out.println("In try block");
throw new NullPointerException();
} catch (NullPointerException npe) {
System.out.println("In catch block");
} finally {
System.out.println("In finally block");
}
}

@Override
protected void finalize() throws Throwable {
System.out.println("In finalize block");
super.finalize();
}

@Override
public void run() {
try {
testMethod();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

////////////////////////////////
public class TestMain2 {
@SuppressWarnings("deprecation")
public static void main(String[] args) {
for (int i = 1; i <= 3; i++) {
new Thread(new TryCatchFinallyTest()).start();
}
}
}

输出结果:

In try block

In try block

In catch block

In finally block

In catch block

In finally block

In try block

In catch block

In finally block

 

我们是期望，finalize方法会被执行的。但是，finalize方法没有被执行。finalize方法，是在该对象被GC回收的时候，被GC调用执行的，而我们不知道GC什么时候进行垃圾回收。

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

 

面对这种，依赖于GC，依赖于GC的回收才执行的方法，除非，你真的有需要，否则，我也觉得，不要使用。

 

引用:

http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#finalize%28%29