Ubinetics Placement Paper -: Java Questions And Answers

Ubinetics Previous Years Solved Sample Placement Papers

1. What will be the output of the following Java code?

   
   class newthread extends Thread
   {
       Thread t;
       newthread()
       {
           t1 = new Thread(this, "Thread_1");
           t2 = new Thread(this, "Thread_2");
           t1.start();
           t2.start();
       }
       public void run()
       {
           t2.setPriority(Thread.MAX_PRIORITY);    
           System.out.print(t1.equals(t2));
       }    
   }
   class multithreaded_programing
   {
       public static void main(String args[])
       {
           new newthread();        
       }
   }
       

   A: truetrue

   B: falsefalse

   C: true

   D: false

   Ans: B

   Explanation:

   This program was previously done by using Runnable interface, here we have used Thread class. This shows both methods are equivalent, we can use any of them to create a thread.

   Output:

   
   $ javac multithreaded_programing.java
   $ java multithreaded_programing
   falsefalse
       

2. Which one of the following is not an access modifier?

   A: Protected

   B: Void

   C: Public

   D: Private

   Ans: B

   Explanation:

   Public, private, protected and default are the access modifiers.

3. What will be the output of the following Java program?

   
   final class A 
   {
       int i;
   }    
   class B extends A 
   {
       int j;
       System.out.println(j + " " + i);  
   }    
   class inheritance 
   {
       public static void main(String args[])
       {
           B obj = new B();
           obj.display();     
       }
   }
       

   A: 2 2

   B: 3 3

   C: Runtime Error

   D: Compilation Error

   Ans: D

   Explanation:

   Class A has been declared final hence it cannot be inherited by any other class. Hence class B does not have member i, giving compilation error.

   Output:

   
   $ javac inheritance.java
   Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
       i cannot be resolved or is not a field
       

4. What is the numerical range of a char data type in Java?

   A: 0 to 256

   B: -128 to 127

   C: 0 to 65535

   D: 0 to 32767

   Ans: C

   Explanation:

   Char occupies 16-bit in memory, so it supports 216 i:e from 0 to 65535.

5. Which of the following methods are methods of the String class? a) delete( ) b) append( ) c) reverse( ) d) replace( ) Answer: d) replace( ) Explanation: The replace() method is part of the String class, while the others are not.
6. Which of the following methods cause the String object referenced by s to be changed? a) s.concat( ) b) s.toUpperCase( ) c) s.replace( ) d) s.valueOf( ) Answer: a) and b) Explanation: concat() and toUpperCase() return new strings; however, they modify the string indirectly since strings in Java are immutable.
7. Is String a wrapper class? a) True b) False Answer: b) False Explanation: String is not a wrapper class. Wrapper classes in Java are used to wrap primitive types, but String is used to represent sequences of characters.
8. What is an Applet? Should applets have constructors? Answer: Applet is a dynamic and interactive program that runs inside a Web page displayed by a Java-capable browser. We don’t have the concept of Constructors in Applets.
9. How can I arrange for different applets on a web page to communicate with each other? Answer: Name your applets inside the Applet tag and invoke AppletContext’s getApplet() method in your applet code to obtain references to the other applets on the page.
10. How do I select a URL from my Applet and send the browser to that page? Answer: Ask the applet for its applet context and invoke showDocument() on that context object.

        Example:
        URL targetURL;
        String URLString;
        AppletContext context = getAppletContext();
        try {
            targetURL = new URL(URLString);
        } catch (MalformedURLException e) {
            // Code for recovery from the exception
        }
        context.showDocument(targetURL);
        

11. Can applets on different pages communicate with each other? Answer: No. Not directly. The applets will exchange the information at one meeting place, either on the local file system or at a remote system.
12. How do Applets differ from Applications? Answer:
    • Appln: Stand Alone
    • Applet: Needs no explicit installation on the local machine
    • Appln: Execution starts with the main() method
    • Applet: Execution starts with the init() method
    • Appln: May or may not have a GUI
    • Applet: Must run within a GUI (Using AWT)
13. What are the Applet’s Life Cycle methods? Explain them? Answer: init() method - Called when an applet is first loaded. Applets have a defined life cycle including the init(), start(), stop(), and destroy() methods.