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Q751. Would you consider creating a constant name for "null" ?

Ans. Objective of constant variable is to provide a context to the value and provide a single point of change. In terms of context, i don't see much need for having constant name for null as null is already self explanatory. In terms of providing single point of change, it doesn't make much sense as it would necessitate that all such placeholders either hold null or a common value.

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Q752. 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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Q753. 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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Q754. 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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Q755. 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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Q756. 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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Q757. 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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Q758. 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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Q759. 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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Q760. Can we call a constructor explicitly , just like a method ?

Ans. No we cannot call a constructor like that.

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Q761. 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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Q762. 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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Q763. 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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Q764. 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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Q765. 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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Q766. 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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Q767. 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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Q768. 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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Q769. 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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Q770. 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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Q771. 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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Q772. 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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Q773. 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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Q774. 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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Q775. What are the examples of immutable objects in Java ?

Ans. Following Classes in Java SE creates immutable objects

String class
Wrapper Classes like Integer, Float etc.
StackTraceElement
Most Enum classes
File Class
Locale Class

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Q776. Can you give real time examples of thread or where thread are actually used ?

Ans. Games are very good examples of threading.You can use multiple objects in games like cars, motor bikes, animals, people etc. All these objects are nothing but just threads that run your game application.

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Q777. What is meant by the statement "Java is turing complete" ?

^{This question is still unanswered. Can you please provide an answer.}

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Q778. Is Java type Safe ?

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Q779. What is Lambda Calculus ?

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Q780. What is Type Inference ? Can you explain with respect to Java ?

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