java mock tests for scjp

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Question 1.

Read the code below carefully.

if( "String".endsWith("")) Sytem.out.println("True");else System.out.println("False");

The code produces

1. True 2. False

Question 2.


if( "String".startsWith("")) Sytem.out.println("True");else System.out.println("False");

The code produces

1. True 2. False

Question 3.


public class TestClass { public static void main(String Args[]) { StringBuffer sb1 = new StringBuffer("String"); StringBuffer sb2 = new StringBuffer("String"); if(sb1.equals(sb2))

{ //lots of code } } }

Is the line marked "lots of code" ever reached?

Question 4.


public class NiceThreads implements Runnable{ public void run() { while(true) { } }

public static void main(String args[]) { NiceThreads nt1 = new NiceThreads(); NiceThreads nt2 = new NiceThreads(); NiceThreads nt3 = new NiceThreads();

nt1.run(); nt2.run(); nt3.run(); }}

1. The code does not compile - "nt2.run() is never reached" 2. The code compiles and runs 3 non ending non demon threads. 3. The code compiles but runs only 1 non ending, non demon thread.

Question 5.

When does the JVM exit?

1. After the main method returns. 2. After all the non demons threads created by the application complete. 3. After all the demon threads created by the application complete 4. When a thread executes System.exit(); 5. When an uncaught exception is thrown in a non demon thread. 6. When an uncaught exception is thrown in a demon thread.

Question 6.

Read the following code, which is a part of a synchronized method of a monitor.

public synchronized void someMethod(){ //lots of code

try { Thread.sleep(500); } catch(InterruptedException e) { //do some crap here. } //more and more code here}

1. The code causes compilation error - sleep cannot be called inside synchronized methods. 2. The code causes compilation error - sleep is not a static method of java.lang.Thread 3. The Thread sleeps for at least 500 milliseconds in this method if not interrupted. 4. When the thread "goes to sleep" it releases the lock on the object. 5. The "sleeping" Threads always have the lock on the Object.

Question 7.

The no-argument constructor provided by the compiler when no constructor is explicitly provided in the code

1. is always public 2. is always "friendly" 3. always defaults to the access modifier provided for the class. 4. depends on the compilation options of javac

Question 8.

Which of the following is the direct base class of java.awt.AWTEvent.

1. java.lang.Object.2. java.util.EventObect

Question 9.

Interface methods can be declared with the following modifiers

1. public 2. none (i.e., no access modifier). 3. private. 4. static 5. native 6. synchronized.

Question 10.

Which of the following are true about the class defined inside an interface

1. it is not possible in the java Laungage. 2. The class is always public. 3. The class is always static. 4. the class methods cannot call the methods declared in the interface. 5. the class methods can call only the static methods declared in the interface.

Question 11.

what does the following expression return?

(0.0 == -0.0)

1. true 2. false

Question 12.

What does the following expression print on the screen?

System.out.println(Math.min(Float.NaN, Float.POSITIVE_INFINITY));

1. NaN 2. Infinity 3. The expression throws a runtime exception - NaN is an illegal argument.

Question 13.

What does the following expression return

Math.max(Float.POSITIVE_INFINITY,Double.POSITIVE_INFINITY);

1. Float.POSITIVE_INFINITY 2. Double.POSITIVE_INFINITY 3. runtime Exception

Question 614.

Read the following code carefully.

public class AStringQuestion{

static String s1; static String s2;

public static void main(String args[]) { s2 = s1+s2;

System.out.println(s2); }}

Attempting to compile and run the code

1. Will cause a compilation error. 2. Runtime Execption - NullPointerException in the 2nd line of the main method. 3. Will compile successfully and print nullnull on the screen. 4. Will compile successfully and print an empty line on the screen. 5. Will compile successfully and print nothing on the screen.

Question 15.


public class AQueryClass{ public static synchronized void method1() { //lots and lots of code here. }

public sychronized void method2() { //lots of code here too. }}

Assuming that all the code inside the method is legal and cannot be a cause for compilation error -

1. An attempt to compile will cause a compilation error. Static methods cannot be synchronized. 2. Compilation will be successfull. The Object instantiated will have a lock which has to be gained by Threads

calling any of the two methods. 3. Compilation will be successfull. There will exist a Class wide lock which will have to be gained by the Thread

calling method1 and an instance lock for each instance which will have to be gained by the Thread making a call to method2 on the Object instance. The class wide lock and the instance lock being independent of each other.

4. Compilation will be successfull. There will exist a Class wide lock which will have to be gained by the Thread calling method1 and an instance lock for each instance which will have to be gained by the Thread making a call to method2 on the Object instance. The class wide lock and the instance lock being mutually exclusive.

Question 16.

Class fields with the following modifiers will not be serialized

1. private 2. static 3. transient 4. protected

Question 67.

Assume that Cat is a class and String[] args is the argument passed to the public static void main(String args[]) method of the class. The class is executed with the following command line string

c:\somedirectory> java Cat

An expression in the main method is as follows

System.out.println(args.length);

1. The above expression will cause a '0' appear on the command line. 2. Will throw a NullPointerException. 3. Will a blank line to appear.

Question 18.

A demon Thread group

1. has only demon threads. 2. can have non demon threads. 3. does not exist after all non demon threads in the group have finished executing. 4. does not exist after all the threads in the group have finished executing.

Question 19.

Assume that th is an instance holding a thread object. th.start() causes the thread to start running and eventually complete its execution. The object reference by th is not accessable any more and is garbage collected when the garbage collecter runs.

1. True 2. False

Question 20.


import java.io.*;

public class OutOut{ public static void main(String args[]) throws IOException {

PrintStream pr = new PrintStream(new FileOutputStream("outfile"));

System.out = pr;

System.out.println("Lets see what I see now??"); }}

1. The code causes a compiler error. out is a declared final in System and cannot be assigned to pr. 2. The code causes a runtime Exception due the assignment to a final variable. 3. The code compiles and runs success fully. A file called "outfile" is created and "Lets see what I see now??" is

printed in the same.

Question 21.

Read the following piece of code carefully

public abstract class AbstractClass{ public AbstractClass() { System.out.println("this is an abstract class constructor!"); }

public void aMethod() { System.out.println("This is in the method in the abstract class"); }

}

Attempting to compile and run the code will cause

1. Compiler error - abstract classes cannot have constructors. 2. Compiler error - the method AbstractClass does not have a valid return type. 3. Compiler error - the class cannot be declared as abstract as it does not have any unimplemented methods. 4. No compiler error - the class is practically not an abstract class and can be instantiated. 5. No compiler error - the class cannot be instantiated directly. It has to be extended to an non-abstract class. The

constructors of the extended class will call the constructor of the abstract class (implicitly or explicitly). 6. No compiler error - the class cannot be instantiated directly. It has to be extended to an non-abstract class. The

constructors of the abstract class will never be called.

Question 22.

Read the following piece of code carefully.

import java.io.IOException;

public class Question72{ public Question72() throws IOException { throw new IOException(); }}

Assume that the defination of Question72E begins with the line

public class Question72E extends Question72

It is required that none of the constructors of Question72E should throw any checked exception.

1. It can be achived by placing the call to the superclass with a super keyword , which is placed in a try block with a catch block to handle the IOException thrown by the super class.

2. It can be achived by avoiding explicit calls to the base class constructor. 3. It cannot be done in the Java Laungage with the above definition of the base class.

Question 23.

Read the following piece of code carefully. (This is an extention to question 72.)

public abstact class Question73 extends Question72{ public abstract void method();}

An attempt to compile the above class definition

1. will cause a compiler error - non-abstract classes cannot be extended to abstract classes. 2. will cause a compiler error - a constructor must be provided which may or may not throw an IOException 3. will cause a compiler error - a constructor must be provided which must throw an IOException or one of its

super types. 4. will not cause any compiler error. The class definition is perfectly legal.

Question 24.


class Base{ Base() { System.out.println("Message 1 : In the base class constructor"); }}

abstract class Derived1 extends Base{ Derived1() { System.out.println("Message 2 : In the abstract class Derived1\'s constructor"); }}

public class Derived2 extends Derived1{ public Derived2() {

System.out.println("Message 3 : In the derived2 class\'s constructor."); } public static void main(String args[]) { Derived2 d2 = new Derived2(); }}

An attempt to compile and run the above code

1. will cause a compiler error. The non-abstract classes cannot be extended to the abstract classes. 2. will cause a compiler error. The abstract classes cannot have constructors defined. 3. will not cause any compiler error. The lines "Message 1..." and "Message 3 ... " are printed on the screen. 4. will not cause any compiler error. The lines "Message 1..." and "Message 2...." and Message 3...." are printed

on the screen.

Question 25.


public class A{ A() { }}

1. The class A can be referenced outside the package in which it is defined. 2. The class A cannot be instantiated outside the package in which it is defined. 3. The class A cannot be extended outside the package in which it is defined. 4. The class A can be referenced, instantiated or extended anywhere. 5. The above code will cause a compiler error. The constructors of public class have to be public.

Question 27.

If the finalize() method of an object is re-references an object so that it becomes in-eligible for garbage collection

1. The compiler will throw an error. 2. The garbage collector "collects" the object anyway. 3. The garbage collector does not collect the object in the present sweep. But when the object becomes eligible for

garbage collection again, its finalize method will not be called by the garbage collector (i.e., if the garbage collector gets a chance to run.). It will simply be garbage collected.

4. The object can never be garbage collected and hence leads to memory-leak. Each time the garbage collector calls finalize before "collecting" the object the object "resurrects" itself.

Question 28.

If a Runtime Exception is thrown in the finalize method -

1. The running application crashes. 2. The exception is simply ignored and the object is garbage collected. 3. The exception is simply ignored, but the object is not garbage collected. 4. The Exception causes the JVM to crash.

Question 29.

The factory class java.util.Collections

1. is public 2. implements the java.util.Collection interface.

Question 30.

import java.io.*;

public class TransientWriter implements Externalizable { private transient String s = "Hope I can ever be persistant!";

public void writeExternal(ObjectOutput oOut) throws IOException { oOut.writeObject(s); } public void readExternal(ObjectInput oIn) throws IOException, ClassNotFoundException { s=(String)oIn.readObject(); }

public String toString() { return s; } }

class K { public static void main(String args[]) throws IOException, ClassNotFoundException { TransientWriter tw = new TransientWriter(); ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("tw.out")); out.writeObject(tw);

ObjectInputStream in = new ObjectInputStream(new FileInputStream("tw.out"));

TransientWriter tw2 = (TransientWriter) in.readObject(); System.out.println(tw2); } }

Attempting to compile and run the above code

1. will cause a compiler error due to the attempt to write a transient object. 2. will cause a runtime exception when an attempt is made to write a transient object. 3. will not cause any runtime error and the transient object is writen to the file named "tw.out". 4. will not cause any runtime error and the transient object is not written to the file named "tw.out". The program

prints a blank line on the screen.

The following code is for Questions 81 and 82

//Contents of File AnInterface.java

public interface AnInterface { public void methodOne() throws Exception; }

//Contents of File AnInterfaceImpl.java

public class AnInterfaceImpl implements AnInterface { public void methodOne() { System.out.println("I will never throw an exception"); } }

Question 31.


public class ATest { public static void main(String args[]) { AnInterface ai = new AnInterfaceImpl(); ai.methodOne(); } }


1. Will cause a compile time error. (Line 5 : Exception must be caught or thrown by main(String)) 2. Will cause a compile time error for Class AnInterfaceImpl. The method methodOne() be declared with

"throws Exception". 3. Will cause no compile time error and print "I will never throw and Exception the screen". 4. Will Cause a run time error .

Question 32.


public class ATest { public static void main(String args[])

{ AnInterfaceImpl ai = new AnInterfaceImpl(); ai.methodOne(); } }


1. Will cause a compile time error. (Line 5 : Exception must be caught or thrown by main(String))

2. Will cause a compile time error for Class AnInterfaceImpl. The method methodOne() be declared with "throws Exception".

3. Will cause no compile time error and print "I will never throw and Exception the screen".4. Will Cause a run time error .

Question 33

Read the code below carefully

//Contents of Constants.java

public class Constants

{

public static final String greetingString="Hello";

}

//Contents of SomeClass.java

public class SomeClass

{

public static void main(String[] args)

{

System.out.println("Greeting String is "+Constants.greetingString);

}

}

The Constants.java file is edited and the greetingString is changed to "Hello World!". The file after editing is shown below.

public class Constants

{

public static final String greetingString="Hello World!";

}

On Compilation of Constants.java and running of the application gives. (Note : The client class SomeClass is not compiled)

1. A RuntimeException due to incompatable change in class Constants2. An Error due to incompatable change in class Constants3. The program terminates normally and "Hello" is printed on the system console.4. The program terminates normally and "Hello World!" is printed on the system console.

Question 34.

Read the code below carefully

import java.util.*;

public class AllFinals { final Vector v; public AllFinals() { } }

The above code will

1. Not compile. Vector v is not initialized. 2. Will compile and throw a RuntimeException 3. Will compile and not throw any Exception during runtime. V is initalized to null.

Question 35.

import java.util.*;

public class AllFinals { { final Vector v; v=new Vector(); } public AllFinals() { }

public void someMethod() { System.out.println(v.isEmpty()); }

}

An attempt to compile and call the someMethod of the above class at runtime will cause

1. A compilation error : v is not initialized in all constructors 2. A compilation error : v is not an instance variable 3. "true" is printed on the console 4. "false" is printed on the console

Question 36.

//Contents of File AllFinals.java import java.util.*;

public class AllFinals { final Vector v; public AllFinals() { v=new Vector(); } public AllFinals(int i) {

}

public void someMethod() { System.out.println(v.isEmpty()); }

}

An attempt to compile the above code will cause

1. A compilation error : The final variable is not initialized in all the constructors. 2. A compilation error : The final instance variable is reassigned after initialization in the constructor 3. No compilation error : But will cause a run time exception (NullPointerException) if someMethod is called on an

instance that was created through the constructor with the integer argument. 4. A compilation error : The final instance variable is not initialized in the declaration

Question 37.

public class A{ final StringBuffer sb = new StringBuffer("I am final"); public A() { }

public StringBuffer getSb() { return this.sb; }

public static void main(String[] args) { A a = new A(); StringBuffer localSB = a.getSb(); localSB.append("...."); localSB = new StringBuffer(); System.out.println(localSB.toString()); }}

Attempting to compile and run the above application will yield

1. A compilation error : Final variable being assigned to a non-final handle. 2. A compilation error : implicitly final localSB being reassigned 3. A Runtime Error : Attempted reassignment to a final handle (localSB) 4. No Errors during compilation and execution. An Empty line is printed on the console.

Question 38.

public class A{ StringBuffer sb = new StringBuffer("I am final"); public A() { } public final StringBuffer getSb() { return this.sb; }

public static void main(String[] args) { A a = new A(); StringBuffer localSB = a.getSb(); localSB.append("...."); localSB = new StringBuffer(); System.out.println(localSB.toString()); }}

Attempting to compile and run the above application will yeild

1. A compilation error : Final variable being assigned to a non-final handle. 2. A compilation error : implicitly final localSB being reassigned 3. A Runtime Error : Attempted reassignment to a final handle (localSB) 4. No Errors during compilation and execution. An empty line is printed on the console.

Question 39.

public class A{ StringBuffer sb = new StringBuffer("I am final"); public A() { } public StringBuffer getSb() { return this.sb; }

public static void main(String[] args) { A a = new A(); final StringBuffer localSB = a.getSb(); localSB.append("...."); localSB = new StringBuffer(); System.out.println(localSB.toString()); }}

Attempting to compile and run the above application will yeild

1. A compilation error : non final variable being assigned to a final handle. 2. No Errors during compilation and execution. "I am final...." is printed on the console. 3. A compilation error : final localSB being reassigned 4. A Runtime Error : Attempted reassignment to a final handle (localSB)

Question 40.

//contents of file A.javapublic class A{ A() { class B { static { System.out.println("I am getting loaded"); } } }

A(int i) { System.out.println("No B this time"); }}

class C{ public static void main(String[] args) { A a = new A(1); }}

Attemping to compile and execute the above Code

1. Compilation error : Inner class inside method cannot have static members or blocks 2. Compilation error : Inner classes cannot be delared inside constructors 3. No compilation error : At runtime Class B is not loaded 4. No compilation error : At runtime class B is loaded and the message "I am getting loaded" is printed on the

console.

Question 41. Read the following code excerpt carefully. //Contents of file A.java public class A{ A() { class B { { System.out.println("I am in no-arg constructor"); } } }

A(int i) { class B { { System.out.println("I am in the arg constructor"); } } new B(); }}

class C{ public static void main(String[] args) { A a = new A(1); }}Which of the following are true

1. A.java cannot be compiled. Duplicate defination of inner class B. 2. A.java compiles without any error. An attempt to run C as an application will cause runtime linkage error.

Duplicate definations of inner class B are found 3. Only one class file corresponding to the inner class B is created in the file system. 4. Two class files corresponding to both inner classes (B) is created in the file system. 5. The classes compile cleanly and on running C as an application causes "I am in the arg constructor" to be

printed on the console

Answers:

1. 1 2. 1 3. No 4. 3 5. 2,4 6. 3,5 7. 3 8. 2 9. 1,2

10. 2,3,4 11. 1 12. 1 13. 2 14. 3 15. 3 16. 2,3 17. 1 18. 2,4 19. 2 20. 1 21. 5 22. 3 23. 3 24. 4 25. 1,2,3 26. 1 27. 3 28. 2 29. 1 30. 3 31. 1 32. 3 33. 3 34. 1 35. 2 36. 1 37. 4 38. 4 39. 3 40. 1 41. 4,5

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