Finalize()在垃圾收集之前被调用。当对象超出作用域时，不调用它。这意味着您无法知道finalize()何时甚至是否会执行。

例子:

如果你的程序在垃圾回收发生之前结束，finalize()将不会执行。因此，它应该被用作备份过程，以确保其他资源的正确处理，或用于特殊用途的应用程序，而不是作为您的程序在其正常运行中使用的手段。

Finalize将打印出类创建的计数。

protected void finalize() throws Throwable {
    System.out.println("Run F" );
    if ( checkedOut)
        System.out.println("Error: Checked out");
        System.out.println("Class Create Count: " + classCreate);
}

main

while ( true) {
    Book novel=new Book(true);
    //System.out.println(novel.checkedOut);
    //Runtime.getRuntime().runFinalization();
    novel.checkIn();
    new Book(true);
    //System.runFinalization();
    System.gc();

如你所见。下面的输出显示了类计数为36时第一次执行的gc。

C:\javaCode\firstClass>java TerminationCondition
Run F
Error: Checked out
Class Create Count: 36
Run F
Error: Checked out
Class Create Count: 48
Run F

Sometimes when it is destroyed, an object must make an action. For example, if an object has a non-java resource such as a file handle or a font, you can verify that these resources are released before destroying an object. To manage such situations, java offers a mechanism called "finalizing". By finalizing it, you can define specific actions that occur when an object is about to be removed from the garbage collector. To add a finalizer to a class simply define the finalize() method. Java execution time calls this method whenever it is about to delete an object of that class. Within the finalize method() you specify actions to be performed before destroying an object. The garbage collector is periodically searched for objects that no longer refer to any running state or indirectly any other object with reference. Before an asset is released, the Java runtime calls the finalize() method on the object. The finalize() method has the following general form:

protected void finalize(){
    // This is where the finalization code is entered
}

使用protected关键字，finalize()类之外的代码可以阻止对finalize()的访问。 务必要理解finalize()是在垃圾收集之前调用的。例如，当对象离开作用域时，它不会被调用。这意味着您无法知道finalize()何时或是否将执行。因此，程序必须提供其他方法来释放系统资源或对象使用的其他资源。不应该依赖finalize()来实现程序的正常运行。

An Object becomes eligible for Garbage collection or GC if its not reachable from any live threads or any static refrences in other words you can say that an object becomes eligible for garbage collection if its all references are null. Cyclic dependencies are not counted as reference so if Object A has reference of object B and object B has reference of Object A and they don't have any other live reference then both Objects A and B will be eligible for Garbage collection. Generally an object becomes eligible for garbage collection in Java on following cases:

该对象的所有引用显式设置为空，例如object = null 对象在块内创建，一旦控件退出该块，引用就会离开作用域。 父对象设置为空，如果一个对象持有另一个对象的引用，并且当您将容器对象的引用设置为空时，子对象或包含对象自动符合垃圾收集的条件。 如果一个对象只有通过WeakHashMap的活动引用，那么它就有资格进行垃圾收集。

正如在https://wiki.sei.cmu.edu/confluence/display/java/MET12-J.+Do+not+use+finalizers上指出的那样，

There is no fixed time at which finalizers must be executed because time of execution depends on the Java Virtual Machine (JVM). The only guarantee is that any finalizer method that executes will do so sometime after the associated object has become unreachable (detected during the first cycle of garbage collection) and sometime before the garbage collector reclaims the associated object's storage (during the garbage collector's second cycle). Execution of an object's finalizer may be delayed for an arbitrarily long time after the object becomes unreachable. Consequently, invoking time-critical functionality such as closing file handles in an object's finalize() method is problematic.

Finalize()在垃圾收集之前被调用。当对象超出作用域时，不调用它。这意味着您无法知道finalize()何时甚至是否会执行。

例子:

如果你的程序在垃圾回收发生之前结束，finalize()将不会执行。因此，它应该被用作备份过程，以确保其他资源的正确处理，或用于特殊用途的应用程序，而不是作为您的程序在其正常运行中使用的手段。