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Java Interview Questions and Answers
Explain garbage collection?
Garbage collection is one of the most important feature of Java. Garbage
collection is also called automatic memory management as JVM
automatically removes the unused variables/objects (value is null) from
the memory. User program cann't directly free the object from memory,
instead it is the job of the garbage collector to automatically free the
objects that are no longer referenced by a program. Every class inherits
finalize() method from java.lang.Object, the finalize() method is called
by garbage collector when it determines no more references to the object
exists. In Java, it is good idea to explicitly assign null into a
variable when no more in use. I Java on calling System.gc() and
Runtime.gc(), JVM tries to recycle the unused objects, but there is no
guarantee when all the objects will garbage collected.
Describe the principles of OOPS.
There are three main principals of oops which are called Polymorphism,
Inheritance and Encapsulation.
Explain the Encapsulation principle.
Encapsulation is a process of binding or wrapping the data and the codes
that operates on the data into a single entity. This keeps the data safe
from outside interface and misuse. One way to think about encapsulation
is as a protective wrapper that prevents code and data from being
arbitrarily accessed by other code defined outside the wrapper.
Explain the Inheritance principle.
Inheritance is the process by which one object acquires the properties
of another object.
Explain the Polymorphism principle.
The meaning of Polymorphism is something like one name many forms.
Polymorphism enables one entity to be used as as general category for
different types of actions. The specific action is determined by the
exact nature of the situation. The concept of polymorphism can be
explained as "one interface, multiple methods".
Explain the different forms of Polymorphism.
From a practical programming viewpoint, polymorphism exists in three
distinct forms in Java:
Method overloading
Method overriding through inheritance
Method overriding through the Java interface
What are Access Specifiers available in Java?
ccess specifiers are keywords that determines the type of access to the
member of a class. These are:
Public
Protected
Private
Defaults
Describe the wrapper classes in Java.
Wrapper class is wrapper around a primitive data type. An instance of a
wrapper class contains, or wraps, a primitive value of the corresponding
type.
Following table lists the primitive types and the corresponding wrapper
classes:
Primitive Wrapper
boolean java.lang.Boolean
byte java.lang.Byte
char java.lang.Character
double java.lang.Double
float java.lang.Float
int java.lang.Integer
long java.lang.Long
short java.lang.Short
void java.lang.Void
Question: Read the following program:
public class test {
public static void main(String [] args) {
int x = 3;
int y = 1;
if (x = y)
System.out.println("Not equal");
else
System.out.println("Equal");
}
}
What is the result?
A. The output is “Equal”
B. The output in “Not Equal”
C. An error at " if (x = y)" causes compilation to fall.
D. The program executes but no output is show on console.
Answer: C
Use the Externalizable interface when you need complete control over
your Bean's serialization (for example, when writing and reading a
specific file format).
No. Earlier order is maintained.
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