SCJP中的一题(关于回收)

最新推荐文章于 2021-06-18 23:35:01 发布

原创最新推荐文章于 2021-06-18 23:35:01 发布 · 911 阅读

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博客给出Java代码示例，包含TestA、TestB和TestAll类。提出在特定代码行后、main方法完成前的相关问题，询问哪些陈述为真。答案选C和D，解释称这是隔离岛的典型例子，相互引用的对象若形成隔离岛可被垃圾回收。

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class TestA {
TestB b;
TestA() {
b = new TestB(this);
}
}
class TestB {
TestA a;
TestB(TestA a) {
this.a = a;
}
}
class TestAll {
public static void main (String args[]) {
new TestAll().makeThings();
// ...code continues on
}
void makeThings() {
TestA test = new TestA();
}
}

Which two statements are true after line 15, before main completes? (Choose two)
A. Line 15 causes a stack overflow.
B. An exception is thrown at runtime.
C. The object referenced by a is eligible for garbage collection.
D. The object referenced by b is eligible for garbage collection.
E. The object referenced by a is not eligible for garbage collection.
F. The object referenced by b is not eligible for garbage collection.

答案是c，d。它是这样解释的：This is a typical example of the island of isolation. On line 15, the two objects TestA and TestB have a eference to one an other. Therefore, the correct answers are C. and D. A key point to remember is that an object that is referenced by another object can be eligible for
garbage collection if the two objects form an island of isolated objects.