问一个java 认证的考题
如下
Which three statements are true? (Choose three)
A. The default constructor initializes method variables.
B. The default constructor has the same access as its class.
C. The default constructor invoked the no-arg constructor of the superclass.
D. If a class lacks a no-arg constructor, the compiler always creates a default constructor.
E. The compiler creates a default constructor only when there are no other constructors
for the class.
Answer: B, C, E
B怎么理解？
还有一题
如下
1. class TestA {
2. TestB b;
3. TestA() {
4. b = new TestB(this);
5. }
6. }
7. class TestB {
8. TestA a;
9. TestB(TestA a) {
10. this.a = a;
11. }
12. }
13. class TestAll {
14. public static void main (String args[]) {
15. new TestAll().makeThings();
16. // ...code continues on
17. }
18. void makeThings() {
19. TestA test = new TestA();
20. }
21. }
Which two statements are true after line 15, before main completes? (Choose tw
o)
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.
标准答案为C, D
不解， 谁可以解释一下啊？
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