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Core Java - Interview Questions and Answers for 'Function' - 20 question(s) found - Order By Newest

Q1. 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){};

^{2017-05-22 21:22:57}

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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Q2. Difference between parameters and arguments ?

^{Admin
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Ans. Parameters are the variables that the method is expected to receive along with the method call. Arguments are the values which are passed on while calling the methods.

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Q3. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)

^{2017-05-23 08:41:54}

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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Q4. Can we overload method as following ?

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

^{2017-05-22 21:27:42}

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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Not frequently asked as it was introduced with Java 8.

Q5. What is the @FunctionalInterface annotation ?

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Ans. This is an informative annotation that specify that the interface is a functional interface. A Function Interface has only one abstract method and many default methods. Compiler generates an error if the interface specified with the annotation doesn't abide by the specifications for functional interface.

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Q6. What is the input to the Reduce function ?

a. One Key and One Value
b. Multiple Keys and Multiple associated Values
c. Multiple Keys and One associated values with each
d. One key and associated values.

^Anonymous

Ans. One key and associated values.

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Q7. How are values passed in Java ? By value or reference ?

Ans. Java only provides pass by value.

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Q8. What are instance methods ?

^{2016-06-03 10:07:50}

Ans. All methods defined in a class that are not marked static are actually instance methods.

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Q9. What are the advantages of using methods in Java ?

^{2017-03-10 10:46:34}

Ans. Likewise classes, methods also provide a way for code reuse and abstraction. Code is reused, clean and easy to understand if classified properly within classes and methods.

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Q10. What are var args ?

or

What is the use of var args ?

^{2017-05-22 21:16:41}

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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Q11. Why following method declarations are not valid ?

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

^{2017-05-22 21:25:36}

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

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Q12. Which method will get called if we call it as method(1)

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

^{2017-05-22 21:32:17}

Ans. Though the call an be bind to either of these but in this case, 1st method will get priority and hence will be called.

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Q13. 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);
      }
   }
}

^{2017-05-23 08:29:28}

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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Q14. 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);
      }
   }
}

^{2017-05-23 08:30:09}

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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Q15. 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);
   }
}

^{2017-05-23 08:32:25}

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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Q16. 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);
   }
}

^{2017-05-23 08:33:56}

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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Q17. 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 ?

^{2017-05-23 08:36:19}

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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Q18. Do you prefer using var args ?

^{2017-05-23 09:04:40}

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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Q19. In the Following code which foo will get called.

foo(Integer i){
}

foo(String s){
}

public static void main(){
passing foo(null);
}

^{2018-01-21 17:16:39}

Ans. ambiguity error

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Q20. How do you define a functional interface?

^{2018-01-22 17:32:13}

Ans. Create interface with the only one non-overriding abstract method and annotate it with @FunctionalInterface

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