Java Tricky Programming Questions

Java Tricky Programming Questions : -
 

Q1)What is the o/p of following program?

public class Test{
 static {
  i=5;
 }
 static int i;
 
 public static void main(String[] args) {
  System.out.println("i value is "+i);
 }
}

Answers
a) 0
b) 5
c) Compilation error
d) 1

Answer is b

Q2) What is the o/p of following program?

public class Test{
  static int i=5;
  public static void main(String[] args) {
    Test test = null;
    System.out.println("i value is "+test.i);
  }
}


Answers
a) 0
b) 5
c) Compilation error
d) NullPointerException

Answer is b. Static variables are related to class and not instance. Hence the instance value doesnt hold good if a static variable is tried to access.

Q3)What is the o/p of following program?

class Father {
protected Father() {
  System.out.println("Created a Father");
 }
}
public class Child extends Father {
  private Child() {
    System.out.println("Inside child");
  }
  public static void main(String args[]) {
    new Child();
  }
}

Answers
a) Inside Child
b) Created a Father
c) Compilation error
d) Created a Father
   Inside Child

Answer is d. As a rule always the parent default constructor is called and then child constructor.

Q4)What is the o/p of following program?

class Father {
 protected Father(String str) {
  System.out.println("Created a Father " +str);
 }
}
public class Child extends Father {
 private Child() {
  System.out.println("Inside child");
 }
 public static void main(String args[]) {
  super("Hi");
  new Child();
 }

a) Inside Child
b) Created a Father
c) Compilation error
d) Created a Father Hi
    Inside Child

Answer is c. As a rule always the parent default constructor should be present if a parameterized constructor is created. In this case create a default constructor for Father class is mssing.

Q5)What is a WeakHashMap?

a) A hashtable-based Map implementation with weak keys
b) A list with weak references to objects
c) A hasttable map with duplictated keys
d) A general purpose hashtable-based implementation to better store.

Answer is a.

Q6)Which of the following is/are true?

a) if("String  ".trim() == "String") 
b) if("   String   ".trim() == "String") 
c) if("String".trim() == "String") 
d) if("Str ing ".trim() == "String")

Answer is c. trim() function is only performed if blankspaces are present   at the beginning or end. If not present it will return the same string. Hence the function will return true.
Bit if the string contains blankspaces, subString() is called to trim the string and return a new String using new operator.

Q7) Which of the following lines allow main method to be executed by ClassLoader?

1: public static String main(String args[]); 
2: protected static void main(String args[]); 
3: final public static void main(String args[]); 
4: public static void main(); 
5: private static void main(String args[]); 
6: public void main(String args[]); 

Answer is 3. Only final,public, static ,void is allowed with main method.

Q8) What is o/p of following program?

public class FinalVar { 
  private int final i; 
  public static void main(String args[]){ 
    System.out.println(new FinalVar().i); 
  } 
} 

a) 1  
b) 0  
c) RunTimeException occurs  
d) Compile time error 'i should be initialized'

Answer is d.Final variable need to be initialized always.