5道关于垃圾回收的题目请高手帮忙指点

[guaiguaibear]

5道关于垃圾回收的题目，请高手指点，选出答案最好说明一下选择的理由！

1.Which of the following statements are true?
A.The automatic garbage collection of the JVM prevents programs from ever running out of memory
B.A program can suggest that garbage collection be performed and force it
C.Garbage collection is platform independent
D.An object becomes eligible for garbage collection when all references denoting it are set to null.

2.Which statements about Java code security are not true?
A.The bytecode verifier loads all classes needed for the execution of a program.
B.Executing code is performed by the runtime interpreter.
C.At runtime the bytecodes are loaded, checked and run in an interpreter.
D.The class loader adds security by separating the namespaces for the classes of the local file system from those imported from network sources.

3.Which statement about the garbage collection mechanism are true?
A.Garbage collection require additional programe code in cases where multiple threads are running.
B.The programmer can indicate that a reference through a local variable is no longer of interest.
C.The programmer has a mechanism that explicity and immediately frees the memory used by Java objects.
D.The garbage collection mechanism can free the memory used by Java Object at explection time.

4.public class X{
public Object m(){
Object o = new Float(3.14F);//line 3
Object [] oa = new Object[1];//line 4
oa[0] = o;//line 5
o=null;//line 6
return oa[0];//line 7
}
}
When is the Float object, created in line 3,eligible for garbage collection?

A.just after line 5.
B.just after line 6
C.just after line 7(that is,as the method returns)
D.never in this method

5.Give the following method:
public void method( ){
String a,b;
a=new String(“hello world”);
b=new String(“game over”);
System.out.println(a+b+”ok”);
a=null;
a=b;
System.out.println(a);
}
In the absence of compiler optimization, which is the earliest point the object a refered is definitely elibile to be garbage collection.

A.before line 5
B.before line 6
C.before line 7
D.before line 9

[caibird1024]

4.c
5.line 3