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- Question
What is the prototype of the default constructor?
public class Test { }
Options- A. Test( )
- B. Test(void)
- C. public Test( )
- D. public Test(void)
- Correct Answer
- public Test( )
Explanation
Option A and B are wrong because they use the default access modifier and the access modifier for the class is public (remember, the default constructor has the same access modifier as the class).Option D is wrong. The void makes the compiler think that this is a method specification - in fact if it were a method specification the compiler would spit it out.
- 1. What will be the output of the program?
public class Test { public static void main(String [] args) { signed int x = 10; for (int y=0; y<5; y++, x--) System.out.print(x + ", "); } }
Options- A. 10, 9, 8, 7, 6,
- B. 9, 8, 7, 6, 5,
- C. Compilation fails.
- D. An exception is thrown at runtime. Discuss
- 2. Which two of the following statements, inserted independently, could legally be inserted into missing section of this code?
- boolean test = (Component instanceof t);
- boolean test = (t instanceof Ticker);
- boolean test = t.instanceof(Ticker);
- boolean test = (t instanceof Component);
import java.awt.*; class Ticker extends Component { public static void main (String [] args) { Ticker t = new Ticker(); /* Missing Statements? */ } }
Options- A. 1 and 4
- B. 2 and 3
- C. 1 and 3
- D. 2 and 4 Discuss
- 3. What will be the output of the program?
class Test { public static void main(String [] args) { int x=20; String sup = (x < 15)? "small" : (x < 22)? "tiny" : "huge"; System.out.println(sup); } }
Options- A. small
- B. tiny
- C. huge
- D. Compilation fails Discuss
- 4. Which statement, inserted at line 10, creates an instance of Bar?
class Foo { class Bar{ } } class Test { public static void main (String [] args) { Foo f = new Foo(); /* Line 10: Missing statement? */ } }
Options- A. Foo.Bar b = new Foo.Bar();
- B. Foo.Bar b = f.new Bar();
- C. Bar b = new f.Bar();
- D. Bar b = f.new Bar(); Discuss
- 5. What line of code should replace the missing statement to make this program compile?
/* Missing Statement? */ public class foo { public static void main(String[]args)throws Exception { java.io.PrintWriter out = new java.io.PrintWriter(); new java.io.OutputStreamWriter(System.out,true); out.println("Hello"); } }
Options- A. No statement required.
- B. import java.io.*;
- C. include java.io.*;
- D. import java.io.PrintWriter; Discuss
- 6. When is the B object, created in line 3, eligible for garbage collection?
void start() { A a = new A(); B b = new B(); a.s(b); b = null; /* Line 5 */ a = null; /* Line 6 */ System.out.println("start completed"); /* Line 7 */ }
Options- A. after line 5
- B. after line 6
- C. after line 7
- D. There is no way to be absolutely certain. Discuss
- 7. Which is a reserved word in the Java programming language?
Options- A. method
- B. native
- C. subclasses
- D. reference
- E. array Discuss
- 8. Which statement is true for the class java.util.ArrayList?
Options- A. The elements in the collection are ordered.
- B. The collection is guaranteed to be immutable.
- C. The elements in the collection are guaranteed to be unique.
- D. The elements in the collection are accessed using a unique key. Discuss
- 9. What will be the output of the program?
public class Test { public static void main(String[] args) { final StringBuffer a = new StringBuffer(); final StringBuffer b = new StringBuffer(); new Thread() { public void run() { System.out.print(a.append("A")); synchronized(b) { System.out.print(b.append("B")); } } }.start(); new Thread() { public void run() { System.out.print(b.append("C")); synchronized(a) { System.out.print(a.append("D")); } } }.start(); } }
Options- A. ACCBAD
- B. ABBCAD
- C. CDDACB
- D. Indeterminate output Discuss
- 10. Which is true about a method-local inner class?
Options- A. It must be marked final.
- B. It can be marked abstract.
- C. It can be marked public.
- D. It can be marked static. Discuss
More questions
Correct Answer: Compilation fails.
Explanation:
The word "signed" is not a valid modifier keyword in the Java language. All number primitives in Java are signed. Hence the Compilation will fails.
Correct Answer: 2 and 4
Explanation:
(2) is correct because class type Ticker is part of the class hierarchy of t; therefore it is a legal use of the instanceof operator. (4) is also correct because Component is part of the hierarchy of t, because Ticker extends Component.
(1) is incorrect because the syntax is wrong. A variable (or null) always appears before the instanceof operator, and a type appears after it. (3) is incorrect because the statement is used as a method (t.instanceof(Ticker);), which is illegal.
Correct Answer: tiny
Explanation:
This is an example of a nested ternary operator. The second evaluation (x < 22) is true, so the "tiny" value is assigned to sup.
Correct Answer: Foo.Bar b = f.new Bar();
Explanation:
Option B is correct because the syntax is correct-using both names (the enclosing class and the inner class) in the reference declaration, then using a reference to the enclosing class to invoke new on the inner class.
Option A, C and D all use incorrect syntax. A is incorrect because it doesn't use a reference to the enclosing class, and also because it includes both names in the new.
C is incorrect because it doesn't use the enclosing class name in the reference variable declaration, and because the new syntax is wrong.
D is incorrect because it doesn't use the enclosing class name in the reference variable declaration.
Correct Answer: No statement required.
Explanation:
The usual method for using/importing the java packages/classes is by using an import statement at the top of your code. However it is possible to explicitly import the specific class that you want to use as you use it which is shown in the code above. The disadvantage of this however is that every time you create a new object you will have to use the class path in the case "java.io" then the class name in the long run leading to a lot more typing.
Correct Answer: There is no way to be absolutely certain.
Correct Answer: native
Explanation:
The word "native" is a valid keyword, used to modify a method declaration.
Option A, D and E are not keywords. Option C is wrong because the keyword for subclassing in Java is extends, not 'subclasses'.
Correct Answer: The elements in the collection are ordered.
Explanation:
Yes, always the elements in the collection are ordered.
Correct Answer: Indeterminate output
Explanation:
It gives different output while executing the same compiled code at different times.
Correct Answer: It can be marked abstract.
Explanation:
Option B is correct because a method-local inner class can be abstract, although it means a subclass of the inner class must be created if the abstract class is to be used (so an abstract method-local inner class is probably not useful).
Option A is incorrect because a method-local inner class does not have to be declared final (although it is legal to do so).
C and D are incorrect because a method-local inner class cannot be made public (remember-you cannot mark any local variables as public), or static.
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