Tricky Mixed Interview Questions
1. What are Wrapper classes in Java?
Java has concept of Wrapper
classes to allow primitive types to be accessed as objects. Primitive types
like boolean, int, double, float etc. have corresponding Wrappers classes –
Boolean, Integer, Double, Float etc. Many of these Wrapper classes are in
java.lang package. Java 5.0 has launched the concept of Autoboxing and Unboxing
in Java for Wrapper classes.
E.g.
public class WrapperTest{
public static void
main(String args[]){
//Converting int into Integer
int count=50;
Integer
i=Integer.valueOf(count);
//converting int into Integer
Integer j=a;
//autoboxing, now compiler will write
Integer.valueOf(count)
internally
System.out.println(count+"
"+i+" "+j);
}
}
2. What is the purpose of native method in Java?
The native keyword is used
for applying to a method to indicate that the method is implemented in native
code using JNI(Java Native Interface). Therefore, native methods allow Java
Developer to directly access platform specific APIs. Often, native methods are
linked to native library.
3. What is System class?
System.class is a final
class provided by java.lang package. It contains several useful class fields
and methods. The purpose of System class is to provide access to system
resources.
4. What is System, out and println in System.out.println method call?
System is a final class
provided by java.lang package. out refers to PrintStream class and a static
member of System class. println is a method of PrintStream class.
5. What is the other name of Shallow Copy in Java?
Object Cloning. A Shallow
Copy just copies the values of references in a Class.
6. What is the difference between Shallow Copy and Deep Copy in Java?
A Shallow copy just copies
the values of the references in the class. A Deep copy copies the values of the
objects as well.
7. What is a Singleton class?
A Singleton class in Java
has maximum one instance of the class present in JVM, all the time. The constructor
of this class is written in such a way that it never creates more than one
object of same class.
8. What is the difference between Singleton class and Static class?
A static class in Java has
only static methods. It is a container of functions. It is created based on
procedural programming design. Singleton class is a pattern in Object Oriented
Design. A Singleton class has only one instance of an object in JVM. This
pattern is implemented in such a way that there is always only one instance of
that class present in JVM.
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