Thread: 50 SCJP Mock Exam Questions with Answers

50 real SCJP Mock Exam Questions. Write your answers down

SCJP Threads

QUESTION : 1

True or false?

Any class that implements the Runnable interface
has to provide the implementation for the following methods:

public void start();
public void run();

1. True.
2. False.

QUESTION : 2

True or false?

A thread that has called the wait() method of an object
still owns the lock of the object.

1. True
2. False

QUESTION : 3

A number of threads of the same priority have relinquished the lock
on a monitor and are in a waiting state after having called the wait()
method of the object. A new thread enters the monitor and calls the
notifyAll() method of the meonitor. Which of these threads will be the
first one to resume?

1. The thread that has been waiting the longest.
2. The thread that was the last one to to exit the monitor.
3. You can never be sure which thread will get to run first.
4. The the first thread that called the wait() method

QUESTION : 4

Which of these are valid contructors of a Thread object.

1. public Thread(Object obj)
2. public Thread(String name)
2. public Thread(Runnable trgt)
4. public Thread(ThreadGroup grp, Runnable trgt, String name)
5. public Thread(ThreadGroup grp, Object ob)

QUESTION : 5

True or false?

If you call the interrupted() method of a thread object twice
the second call will always return false.

1. True
2. False

QUESTION : 6

True or false?

If you call the isInterrupted() method of a thread object twice
the second call will always return false.

1. True
2. False

QUESTION : 7

Which of the following are methods of the Thread class.

1. public void run()
2. public void start()
3. public void exit()
4. public final void setAccess()
5. public final void setPriority(int priNbr)
6. public final int getPriority()

QUESTION : 8

Consider the following class

      public class Test implements Runnable{
      public void run(){}
      }

True or False?

Creating an instance of this class and calling its run() method
will spawn a new thread.

1. True
2. False

QUESTION : 9

True or false?

A Thread object has a method called notify().

1. False
2. True

QUESTION : 10

Calling the destroy() method of a thread object relases all the locks held by
the thread ?

1. True
2. False


SCJP Collections

QUESTION : 1

What is the result of attempting to compile and run the following code?

  public class Test1{
     public static void main(String[] args)
     {
     Integer int1 = new Integer(10);
     Vector vec1 = new Vector();
     LinkedList list = new LinkedList();
     vec1.add(int1);
     list.add(int1);
     if(vec1.equals(list)) System.out.println("equal");
     else  System.out.println("not equal");
      }
  }

1. The code will fail to compile.
2. Runtime error due to incompatible object comparison
3. Will run and print "equal".
4. Will run and print "not equal".

QUESTION : 2

What is the result of attempting to compile and run the following code?

           public class Test {
 
              public static void main(String[] args){
               Integer a = new Integer(4);
               Integer b = new Integer(8);
               Integer c = new Integer(4);
               HashSet hs = new HashSet();
               hs.add(a);
               hs.add(b);
               hs.add(c);
               System.out.println(hs);
              }
         }

1. Will print [8, 4]
2. Will print [4, 8, 4]
3. Will print [8, 4, 4]

QUESTION : 3

What is the result of attempting to compile and run the following code?

           public class Test {
 
              public static void main(String[] args){
               Integer a = new Integer(4);
               Integer b = new Integer(8);
               Integer c = new Integer(4);
               TreeSet hs = new TreeSet();
               ts.add(a);
               ts.add(b);
               ts.add(c);
               System.out.println(ts);
              }
         }

1. Will print [8, 4]
2. Will print [4, 8, 4]
3. Will print [8, 4, 4]
4. Will print [4, 8]
5. Will print [4, 4, 8]

QUESTION : 4

What will this print out ?

           public class Test {
 
              public static void main(String[] args){
               Integer a = new Integer(8);
               Integer b = new Integer(4);
               Integer c = new Integer(4);
               Vector vec = new Vector();
               Iterator itr;
               vec.add(a);
               vec.add(b);
               vec.add(c);
               itr = vec.iterator();
                  while (itr.hasNext()) {
                   System.out.println("" + itr.next());
                  }
              }
         }

1. 8 , 4 and 4
2. 4 , 4 and 8
3. 8 and 4
4. 4 and 8

QUESTION : 5

Which of these statements are true?

1. HashTable is a sub class of Dictionary
2. ArrayList is a sub class of Vector
3. LinkedList is a subclass of ArrayList
4. Stack is a subclass of Vector

QUESTION : 6

Which of these statements are true?

1. LinkedList extends List
2. AbstractSet extends Set
3. HashSet extends AbstractSet
4. WeakHashMap extends HashMap
5. TreeSet extends AbstractSet

QUESTION : 7

Which of these statements are true?

1. A HashSet does not permit duplicates
2. A Vector permits duplicates
3. A TreeSet is an ordered Set
4. A LinkedList is sorted in descending order
5. A LinkedList is sorted in ascending order

QUESTION : 8

True or False?

A WeakHashMap is synchronized.

1. True
2. False

QUESTION : 9

True or False?

A Set rejects duplicates and is ordered

1. True
2. False

QUESTION : 10

Select the true statements

1. AbstractSet extends AbstractCollection
2. AbstractList extends AbstractCollection
3. HashSet extends AbstractSet
4. Vector extends AbstractList
5. AbstrctSequentialList extends AbstractList
6. LinkedList extends AbstrctSequentialList


SCJP Object Oriented Programming

QUESTION : 1

What is the result of compiling and running this program?

      class Mammal{
         void eat(Mammal m){
         System.out.println("Mammal eats food");
         }
      }
      class Cattle extends Mammal{
         void eat(Cattle c){
         System.out.println("Cattle eats hay");
         }
      }
 
      class Horse extends Cattle{
          void eat(Horse h){
          System.out.println("Horse eats hay");
          }
      }
      public class Test{
        public static void main(String[] args){
          Mammal h = new Horse();
          Cattle c = new Horse();
          c.eat(h);
        }
      }

1. prints "Mammal eats food"
2. prints "Cattle eats hay"
3. prints "Horse eats hay"
4. Class cast Exception at runtime.

QUESTION : 2

Consider the following class hierarchy.

1. interface A{
2. public void method1();
3. }
4. class One implements A{
5. public void method1(){
6. System.out.println("hello");
7. }
8. }
9. class Two extends One{}
10. public class Test extends Two{
11. public static void main(String[] args)
12. {
13. A a;
14. Two t = new Two();
15. a = t;
16. a.method1();
17. }
18. }

What will be the outcome on attempting to compile and run this ?

1. Compiles and runs printing out "hello".
2. Compilation error at line 16.
3. The compiler raises an objection to the assignment at line 15.
4. Throws a NoSuchMethodException at runtime.

QUESTION : 3

What will happen if you try to compile and run this?

 interface A{
 public void innerMeth();
 }
        public class Test {
   A a;
   int memVar = 1;
          void aMethod(){
                 a = new A(){
                 public void innerMeth(){
                 System.out.println(memVar);
                 } };
    }
 
           public static void main(String[] args){
            Test t = new Test();
             t.a.innerMeth();
            }
          }

1. Compiler error.
2. NoSuchMethodException at runtime.
3. Compiles and runs printing 1
4. Throws a NullPointerException at runtime.

QUESTION : 4

What will happen if you try to compile and run this code?

         class Rectangle{
           public int area(int length , int width) {
             return  length * width;
           }
          }
 
         class Square extends Rectangle{
            public int area(long length , long width) {
            return  (int) Math.pow(length ,2);
           }
         }
        class Test{
          public static void main(String args[]) {
           Square r = new Square();
           System.out.println(r.area(5 , 4));
          }
        }

1. Will not compile.
2. Will compile and run printing out 20
3. Runtime error
4. Will compile and run printing out 25

QUESTION : 5

What will be the result of attempting to compile and run this.

     class Base{}
     class Derived extends Base{}
     public class Test {
       public static void main(String[] args){
         Derived d = (Derived) new Base();
       }
     }

1. Will not compile
2. Compiles and runs without error.
3. Runtime error

QUESTION : 6

What will this program print out?

      class Base{
        int value = 0;
        Base(){
        addValue();
        }
        void addValue(){
        value += 10;
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
      Derived(){
       addValue();
      }
     void addValue(){
     value +=  20;
      }
    }
    public class Test {
      public static void main(String[] args){
          Base b = new Derived();
          System.out.println(b.getValue());
      }
    }

1. 10
2. 20
3. 30
4. 40

QUESTION : 7

Almost the same code as in the previous question.
The only difference is the methods are static now.
What will it print now?

   class Base{
      static  int value = 0;
        Base(){
        addValue();
        }
    static void addValue(){
        value += 10;
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
      Derived(){
       addValue();
      }
    static void addValue(){
     value +=  20;
      }
    }
    public class Test {
      public static void main(String[] args){
          Base b = new Derived();
          System.out.println(b.getValue());
      }
    }

1. 10
2. 20
3. 30
4. 40

QUESTION : 8

What is the result of attempting to compile and run this?

      interface ITest{
           public void setVal();
      }
      public class Test {
          private String a;
          void aMethod(){
          final String b;
          ITest it = new ITest() {
               public void setVal(){
               a = "Hello";
               b = " World";
               }};
          it.setVal();
          System.out.println(a + b);
          }
          public static void main(String[] args) {
          Test t = new Test();
          t.aMethod();
          }
       }

1. Code will not compile
2. Run time error
3. Will compile and run printing "Hello"
4. Will compile and run without any output

QUESTION : 9

What is the result of attempting to compile and run this?

         class Base{
              String s = "Base";
              String show(){
              return s;
              }
         }
         class Derived extends Base{
              String s = "Derived";
              }
         public class Test {
              void print(Base b){
              System.out.println(b.show());
              }
              void print(Derived d){
              System.out.println(d.show());
              }
              public static void main(String[] args){
              Test t = new Test();
              Base b = new Derived();
              t.print(b);
              }
         }

1. Code will not compile
2. Run time error
3. Will compile and run printing "Derived"
4. Will compile and run printing "Base"

QUESTION : 10

What is the result of attempting to compile and run this ?

    interface ITest{
     public void setVal();
    }
    public class Test {
      private String a;
      void aMethod(){
      final String b = " World";
      ITest it = new ITest() {
                   public void setVal(){
                   a = "Hello" + b;
                   }};
      it.setVal();
      System.out.println(a);
      }
      public static void main(String[] args) {
      Test t = new Test();
      t.aMethod();
      }
    }

1. Code will not compile
2. Run time error
3. Will compile and run printing "Hello World"
4. Will compile and run printing "Hello"


SCJP Language Fundamentals

QUESTION : 1

You have the following code in a file called Test.java

    class Base{
       public static void main(String[] args){
       System.out.println("Hello");
       }
    }
 
    public class Test extends Base{}

What will happen if you try to compile and run this?

1. It will fail to compile.
2. Runtime error
3. Compiles and runs with no output.
4. Compiles and runs printing "Hello"

QUESTION : 2

What is the result of trying to compile and run the following code?

         public final static void main(String[] args){
         double d = 10.0 / -0;
          if(d == Double.POSITIVE_INFINITY)
           System.out.println("Positive infinity");
           else
           System.out.println("Negative infinity");
         }

1. output Positive infinity
2. output Negative infinity
3. Will fail to compile
4. Runtime exception

QUESTION : 3

What is the result that will be printed out?

     void aMethod()
     {
     float f = (1 / 4) * 10;
     int i = Math.round(f);
     System.out.println(i);
     }

1. 2
2. 0
3. 3
4. 2.5
5. 25

QUESTION : 4

Which of the following are valid declarations?

Note : None of the literals used here
contain the character O they are all zeroes.

1. int i = 0XCAFE;
2. boolean b = 0;
3. char c = 'A';
4. byte b = 128;
5. char c = "A";

QUESTION : 5

What is the result of trying to compile and run this program?

    public class Test{
       public static void main(String[] args){
        int[] a = {1};
        Test t = new Test();
        t.increment(a);
        System.out.println(a[a.length - 1]);
       }
       void increment(int[] i){
       i[i.length - 1]++;
       }
    }

1. Compiler error.
2. Compiles and runs printing out 2
3. Compiles and runs printing out 1
4. An ArrayIndexOutOfBounds Exception at runtime

QUESTION : 6

What will happen if you try to compile and run this?

   public class Test{
      static{
       print(10);
       }
     static void print(int x){
       System.out.println(x);
       System.exit(0);
      }
    }

1. Compiler error.
2. Will throw a NoSuchMethod error at runtime.
3. It will compile and run printing out "10"
4. It will run with no output.
5. It will run and print "10" and then crash with an error.

QUESTION : 7

Is this legal?

      long longArr[];
      int intArr[] = { 7 ,8 , 9};
      longArr = intArr;

1. Yes
2. No

QUESTION : 8

True or False?

The range of a byte is from -127 to 128

1. True
2. False

QUESTION : 9

Identify the valid assignments.

1. float f = \u0038;
2. long L2 = 2L;
3. float f = 1.2;
4. char c = '/u004E';
5. byte b = 100;

QUESTION : 10

What is the result of trying to compile and run the following code?

         public static void main(String[] args){
         double d = 10 / 0;
         if(d == Double.POSITIVE_INFINITY)
           System.out.println("Positive infinity");
         else
           System.out.println("Negative infinity");
         }

1. output Positive infinity
2. output Negative infinity
3. Will fail to compile
4. Runtime exception


SCJP java.lang

QUESTION : 1

What is the result of attempting to compile and run this?

         public class Test {
              public static void main(String[] args){
              String s = "HelloWorld".substring(5,10);
              System.out.println(s);
              }
         }

1. The code will fail to compile.
2. Compile and run printing out "orld".
3. Compile and run printing out "oworl"
4. Compile and run printing out "World"
5. Run time exception

QUESTION : 2

Select one right answer.
-----------------------
What is the result of attempting to compile and run this ?

   1.    public class Test {
   2.     public static void main(String[] args){
   3.      Test t = new Test();
   4.      char c = 4 * 4;
   5.      String s = "bead";
   6.      s = t.pearl(s);
   7.      System.out.println(Byte.parseByte(s,c));
          }
   8.     String pearl(String s){
   9.      return s.substring(0,1);
          }
        }

1. Compiler error caused by line 4.
2. Compiler error caused by line 7.
3. Compiler error caused by line 9.
4. Compiles and throws a NumberFormatException at runtime.
5. Compiles and runs printing out a number.
6. Compiles and runs printing out an alphabet.

QUESTION : 3

What is the value of d that will be printed out.

    public class Test {
      public final static void main(String[] args)
      {
      double d = - 22.22222;
      System.out.println(Math.ceil(d));
      }
    }

1. 22
2. 22.0
3. -22
4. -23
5. -22.0
6. 23.0

QUESTION : 4

What is the result of attempting to compile and run this ?

    public class Test {
      public static void main(String[] args)
      {
      StringBuffer a =  "Hello";
      StringBuffer b = a.append("World");
      System.out.println(a);
      }
    }

1. It will print "World"
2. It will print "HelloWorld"
3. It will print "Hello World"
4. The code will not compile.
5. It will print "Hello"
6. It will throw a runtime exception

QUESTION : 5

Which of the follwing are valid methods of the String class.

1. String append(String s);
2. int length();
3. String toString(String str);
4. String trim();
5. int indexOf(int ch);
6. String append(char c);

QUESTION : 6

What is the result of attempting to compile and run this?

    public class Test {
      public static void main(String[] args)
      {
      Float f = new Float(32D);
      System.out.println(f);
      }
    }

1. Does not compile
2. Compiles and runs printing out "32"
3. Compiles and runs printing out "32.0"
4. Compiles but throws an error at runtime

QUESTION : 7

What is the result of attempting to compile and run this?

         public class Test {
 
              public static void main(String[] args){
               byte a = 10;
               Byte b    = new Byte(a);
               Byte c    = new Byte(11);
               System.out.println(b.compareTo(c));
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "false"
4. Runs and prints "0"
5. Runs and prints "1"
6. Runs adn prints "-1"

QUESTION : 8

What is the result of attempting to compile and run this?

 public class Test {
 
              public static void main(String[] args){
               Float f = new Float(16/0);
               System.out.println(f.isNaN());
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "false"
4. Runs and prints "true"

QUESTION : 9

What is the result of attempting to compile and run this ?

         public class Test {
 
              public static void main(String[] args){
               Number n = new Number(16);
               Float f  = new Float(16);
               System.out.println(n.equals(f));
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "false"
4. Runs and prints "true"

QUESTION : 10

What is the result of attempting to compile and run this?

         public class Test {
 
              public static void main(String[] args){
              Integer i  = new Integer(256);
              System.out.println(i.byteValue());
              }
         }

1. Compiler error
2. Runtime error
3. Runs and prints "256"
4. Runs and prints "0"
5. Runs and prints "127"


-------------------

Good luck!!

THE ANSWERS TO THE MOCK EXAM QUESTIONS ARE BELOW. PLEASE DON'T SCROLL DOWN IF YOU DON'T WANT TO KNOW!

SCJP Threads

QUESTION : 1

ANS : 2

QUESTION : 2

ANS : 2

QUESTION : 3

ANS : 3

QUESTION : 4

ANS : 2,3,4

QUESTION : 5

ANS : 1

QUESTION : 6

ANS : 2

QUESTION : 7

ANS : 1,2,5,6

QUESTION : 8

ANS : 2

QUESTION : 9

ANS : 2

The Thread class has a method notify() inherited from Object.

QUESTION : 10

ANS : 2


SCJP Collections

QUESTION : 1

ANS : 3

QUESTION : 2

ANS : 1

QUESTION : 3

ANS : 4

QUESTION : 4

ANS : 1

QUESTION : 5

ANS : 1,4

QUESTION : 6

ANS : 3,5

QUESTION : 7

ANS : 1,2,3

QUESTION : 8

ANS : 2

QUESTION : 9

ANS : 2

QUESTION : 10

ANS : 1,2,3,4,5,6


SCJP Object Oriented Programming

QUESTION : 1

ANS : 1

The method that will be called is the one
from class Mammal. The reasons are quite obvious.

QUESTION : 2

ANS : 1

Object reference conversion is possible here.
The old type which is class can be assigned
to an interface type as long as the class implements
that interface.

QUESTION : 3

ANS : 4

You will get a NullPointerException because the
inner class object gets assigned to the reference a
only after the aMethod() runs. You can prevent
the exception by calling t.aMethod() before the
inner anonymous class method is called.

QUESTION : 4

ANS : 1

This code will fail to compile because the
compiler cannot resolve the method call here.

QUESTION : 5

ANS : 3

QUESTION : 6

ANS : 4

QUESTION : 7

ANS : 3

QUESTION : 8

ANS : 1

QUESTION : 9

ANS : 4

QUESTION : 10

ANS : 3


SCJP Language Fundamentals

QUESTION : 1

ANS : 4

This will compile and print "Hello"
The entry point for a standalone java program is
the main method of the class that is being run.
The java runtime system will look for that method
in class Test and find that it does have such a method.
It does not matter whether it is defined in the class itself
or is inherited from a parent class.

QUESTION : 2

ANS : 1

There is no such thing as a positive or negative zero.
Hence the result is always positive infinity.

QUESTION : 3

ANS : 2

The result of 1/4 will be zero because integer
divion is carried out on the operands.
If you need to obtain a fractional value
you need to use either a float or double literal
as in 1F / 4F.

QUESTION : 4

ANS : 1,3

1. is correct as it is a valid hexadecimal number. 2. is wrong
because you can only assign the values true and false to them
4 is wrong because 128 is beyond the range of a byte. 5 is wrong
because "A" is not a char it is a String.

QUESTION : 5

ANS : 2

You are passing a reference to an array as
the argument to the method. The method may not
modify the passed object reference but it can modify
the object itself.

QUESTION : 6

ANS : 3

This will run, print a message and terminate gracefully.
The runtime system needs to load the class before it can look
for the main method. So the static initializer will run first
and print "10". Immediately after that System.exit(0) will be called
terminating the program before an error can be thrown.

QUESTION : 7

ANS : 2

You cannot assign a reference to an array of primitives
to another unless they contain the same primitive types.

QUESTION : 8

ANS : 2

Correct answer/s : 2
The statement is false. The range of an array
is from - 128 to 127

QUESTION : 9

ANS : 1,2,4,5

1 is correct because \u0038 is unicode for nbr 8.
3 is wrong because 1.2 is a double literal.
4. is a little sneaky perhaps. The
unicode escape character is incorrect

QUESTION : 10

ANS : 4

Division by zero on integer literals will throw
a runtime error.


SCJP java.lang

QUESTION : 1

ANS : 4

QUESTION : 2

ANS : 5

1. Is wrong because it is legal to assign integer
literal to a char variable as long as the value
does not exceed the range of a char.
2. Is wrong because parseByte(String s , int radix)
will accept any native numeric type that is not
wider than an int.
3 and 6 are just nonsense.
4. Is wrong because the the character b falls within
the radix range specified by the second parameter.

QUESTION : 3

ANS : 5

QUESTION : 4

ANS : 4

QUESTION : 5

ANS : 2,4,5

QUESTION : 6

ANS : 3

QUESTION : 7

ANS : 1

QUESTION : 8

ANS : 2

QUESTION : 9

ANS : 1

QUESTION : 10

ANS : 4

I just found this old thread in an unused forum. Thought i'd move and bump it