Core Java - Interview Questions and Answers for 'Declaration' | Search Interview Question

Core Java - Interview Questions and Answers for 'Declaration' - 16 question(s) found - Order By Newest

Q1. What do you mean by "Java is a statically typed language" ?

Ans. It means that the type of variables are checked at compile time in Java.The main advantage here is that all kinds of checking can be done by the compiler and hence will reduce bugs.

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Q2. What is the difference between declaration, instantiation and initialization ?

Core Java

Ans. Declaration is intimation to the compiler about the nature of Data a reference is going to hold.

For example - List myList;

Instantiation is reservation of memory.

For example

myList = new ArrayList();

Initialization or construction is setting the default values for member elements.

For example

myList = new ArrayList(mySet);

** Example 2nd is both for instantiation as well as initialization. The only difference is that 2nd will initialized the member elements to their default values whereas 3rd will initialized it with the elements from set.

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Q3. Which of the following are valid declarations

1. void method(int... x){};
2. void method(int.. x){};
3. void method(int.. .x){};
4. void method(int ...x){};
5. void method(int... x){};
6. void method(int ... x){};
7. void method(int x, int... y){};
8. void method(int... x, int y){};
9. void method(int... x,int... y){};

Core Java

Ans. 1st is a valid and standard declaration.

2nd results in compilation error as only 2 dots are there.

3rd results in compilation error as three dots are not consecutive and broken.

4 through 6 may not be standard and ideal way of declarations but they are valid and will compile and work fine.

7 is valid declaration.

8 and 9 will result in compilation error as var args can only be provided to last argument.

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Q4. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)

Core Java

Ans. First expects the argument as a string array whereas second expects variable number of string arguments or a string array.

So we can call both by providing string array as an argument but second can be called with 0 to n string arguments which cannot be done for first.

for example - We can call second method with any of following

method();
method("Hello");
method("Hello","World");
method(new String[4]);

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Q5. Can we overload method as following ?

void method(int... x){};
void method(int[] x){};

Core Java

Ans. No. Because java internally treats var args as arrays and hence both method declarations will generate the same byte code and hence would result in ambiguity while determining call binding.

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Q6. If everything is an object , Cant we declare every object as

Object obj = new String();

Core Java

Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc.

We cannot access methods defined in String class or in any class in hierarchy between String and Object.

For example - we cannot do obj.append("abc") as it will now give compile time error.

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Q7. Do you prefer using var args ?

Core Java

Ans. Though var args are used rarely but they are pretty useful if a method is expected to receive variable number of arguments. For example - it's pretty useful for the main method as the caller has the flexibility to provide arguments in infinite ways.It provides a convenience and flexibility to the caller.

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Q8. What is the difference between int[] x; and int x[]; ?

Core Java

Ans. No Difference. Both are the acceptable ways to declare an array.

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Q9. What are var args ?

or

What is the use of var args ?

Core Java

Ans. Var args is the feature of Java that allows a method to have variable number of arguments. Var args are used when we are not sure about the number of arguments a method may need. Internally java treats them as array.

Declarations of methods with var args

void method(int... x){};
void method(int x, int... y){};

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Q10. Why following method declarations are not valid ?

void method(int... x, int y){};
void method(int... x,int... y){};

Core Java

Ans. Because var args are not only allowed with the last argument in the method declaration.

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Q11. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello","World");
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }
}

Core Java

Ans. No, It will compile and execute perfectly fine. As we are using method with var args , we can call it with 0 to n arguments.

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Q12. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method();
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }
}

Core Java

Ans. This will compile fine as we can provide 0 arguments for a var arg but will print nothing upon execution.

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Q13. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello");
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }

   private static void method(String arg){
      System.out.println(arg);
   }
}

Core Java

Ans. It will compile fine and the method call will bind to method with specific argument and not with var arg

i.e private static void method(String arg)

It will print "Hello" upon execution

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Q14. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello");
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }

   private static void method(String[] arg){
      System.out.println(arg);
   }
}

Core Java

Ans. Yes, it will give compilation error and java will complain about duplicate method. Java treat var args internally as arrays and hence would result in same byte code for both method's syntax.

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Q15. Will this code work

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello","World");
   }

   private static void method(String[] arg){
      System.out.println(arg);
   }
}

What all possible changes we can make to method signature to make it work ?

Core Java

Ans. It won't work as java won't find the method definition for method with 2 arguments.

We can either declare the method as

private static void method(String arg,String arg2)

or

private static void method(String... arg)

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Q16. Can a source file contain more than one class declaration ?

Core Java

Ans. Yes, but only one of them can be declared public.

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