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Q541. Do you prefer using var args ?

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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Q542. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)

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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Q543. 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 ?

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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Q544. 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);
   }
}

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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Q545. 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);
   }
}

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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Q546. 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);
      }
   }
}

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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Q547. 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);
      }
   }
}

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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Q548. Can we catch errors in Java ?

Ans. Yes we can

try {
// code
} catch (Error ex) {
// handling code
}

but we shouldn't ideally do that as errors are mostly JVM based and not application based and there is rarely we can do something about it. Very likely catching and not re throwing would lead to muting their response or trace.

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Q549. Is it ok to use optional everywhere just to get over nullpointerexception ?

Ans. Optional is to be used for arguments / atrributes which are indeed optional i.e the request should continue even if they aren't provided. It should not be used for mandatory attributes or arguments as we would like application to shout out ( with error message / exception trace ) to signify a problem.

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Q550. Which method will get called if we call it as method(1)

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

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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Q551. Can we overload method as following ?

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

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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Q552. Why following method declarations are not valid ?

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

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

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Q553. 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){};

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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Q554. What are var args ?

or

What is the use of var args ?

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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Q555. What happens when you assign a pre initialized reference some other object ?

Ans. Now the reference points to a new object in memory. If that was the only reference for the previous object , it will be marked for garbage collection.

Foe example -

Object obj = new Object();
obj = new Object();

object created in first line will be eligible for garbage collection after line 2 as it looses all it's handlers.

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Q556. Which of the following is valid greater than and equal to operator in Java ?

>=
=>

Ans. >=

=> will result in error.

=> somewhat looks like lambda operator "->"

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Q557. Java doesn't provide exclusive access to memory like C/C++ and other lower level languages ? What are the advantanges and disadvantages ?

Ans. Yes, doesn't provide exclusive access as we cannot allocate and deallocate memory exclusively as Java internally manages it. The advantage of this is that it relieves the coder for such tasks and helps protect from many bugs that may get introduced with imperfect coding. Moreover as java garbage collector collects all unclaimed memory or objects, it helps the application from memory leaks.

On the flip side , as coder doesn't have extensive excess to memory , it is upto java to decide on the state for programming construct and data storage and hence may introduce some security risks. For example - Java keeps string literals in string pool and there is no exclusive way to remove it and hence may stay and sensitive data in string pool may introduce security issues. Moreover when we overwrite a value or object for a variable / reference, it is upto java to purge those values and hence it may stay in memory for a while till java decide that it is no longer referenced and hence should be removed and hence makes it vulnerable for inappropriate access.

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Q558. Which of following is / are valid static final declaration ?

public static final String MAX_NUM = "10";
public static final Object NULL = null;
public static final MathContext MATH_CONTEXT = new MathContext(2,RoundingMode.CEILING);

Ans. All are valid declarations.

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Q559. Make the following class immutable

public class Employee {

   private long employeeId;

   private String employeeName;

   public long getEmployeeId() {
      return employeeId;
   }

public void setEmployeeId(long employeeId) {
      this.employeeId = employeeId;
   }

   public String getEmployeeName() {
      return employeeName;
   }

public void setEmployeeName(String employeeName) {
      this.employeeName = employeeName;
   }
}

Ans. public class Employee {

   private long employeeId;

   private String employeeName;

   public Employee(long employeeId,String employeeName){
      this.employeeId = employeeId;
      this.employeeName = employeeName;
   }

   public long getEmployeeId() {
      return employeeId;
   }

   public long getEmployeeName() {
      return employeeName;
   }
}

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Q560. What is the difference between reference and object ?

Ans. Object is an entity in Java , i.e which has a state ( instance variables ) and methods attached to it ( static or non static , through class definition ). References are the identifiers that are used to point to objects.

For example -

Employee emp = new Employee();
emp = new Employee();

In this code, emp is the reference that gets assigned to the new object created by the new operator. In the second line , we have assigned the same reference to another object. So with these 2 lines of code, we have 2 objects in memory with reference emp now pointing to second object.

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Q561. Can we call a constructor explicitly , just like a method ?

Ans. No we cannot call a constructor like that.

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Q562. Is this constructor overloading ?

What is the difference between the 2 methods in Java ?

Class BuggyBread {

BuggyBread(){
}
void BuggyBread(int x){
}
}

Ans. No, first method is a constructor whereas the second method is just a normal method. There is no way a constructor can be called explicitly and hence all explicit calls to BuggyBread() would result in compilation error.

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Q563. What is the difference between the 2 methods in Java ?

Class BuggyBread {

BuggyBread(){
}
void BuggyBread(){
}
}

Ans. BuggyBread method without any return type is the constructor which get's called upon object creation whereas BuggyBread method with return type of void is just another method that needs to be called explicitly for it's invocation.

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Q564. Does all methods need to have a return type ? Is it applicable to constructors too ?

Ans. All methods are not expected to return something but Yes, all methods are expected to have a return type. If a method returns nothing, it can be declared with the return type void.

Constructors are not expected to have any return types , not even void.

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Q565. What is void in Java ?

Ans. void is a return type which indicates that the method returns nothing but returns the control to the line next to the method call. All methods need to have a return type and hence a method returning nothing needs to be declared void.

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Q566. What is equals method in Java ?

Ans. equals is the method of Object class that is overridden by the classes to specify object equality criteria.

As every class extends Object class, the default implementation of equals is carried to them. Default implementation specified in the Object class is that two objects are treated equal if they are same.

i.e

Object x = new Object();
Object y = new Object();
x.equals(y); // false
x=y;
x.equals(y); // true

i.e x.equals(y) if only x==y

Now every class has the option to specify their object equality by overriding equals method. For example - String class has implemented in a manner if the string value contained in them is exactly same.

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Q567. What is the purpose of String Pool ? Don't you think it's a performance overhead to have unnecessary check for string in string pool ?

Ans. String Pool makes Java more memory efficient by providing a reusable place for string literals. It might be a little performance inconvenience but results in good amount memory saving.

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Q568. What is a blank final variable ? Can we initialize a blank final variable ?

Ans. A final variable that is not initialized while declaration is a blank final variable.

Yes, we can initialize it within a constructor.

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Q569. What is a platform ? Is Java a Software or Hardware platforms ?

Ans. Platform is the environment in which a program runs. Java provides a software platform for running JVM based applications and programs.

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Q570. What is the difference between following two segments of code

Code 1

int x = 4 * 3;
int y = x * 5;

Code 2

int y = 4 * 3 * 5;

Ans. Both will produce the same output but 1st will consume more resources in terms of memory ( for maintaining intermediate value ) and computing power ( as single mathematical calculation with more operands is more effective than multiple calculations with broken down operands )

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