What is a native method?
A native method is a method that is implemented in a language
other than Java.
In System.out.println(), what is System, out and println?
System is a predefined final class, out is a PrintStream
object and println is a built-in overloaded method in
the out object.
What are Encapsulation, Inheritance and Polymorphism
Or Explain the Polymorphism principle. Explain the different forms of
Polymorphism.
Polymorphism in simple terms means one name many forms. Polymorphism
enables one entity to be used as a general category for different types of
actions. The specific action is determined by the exact nature of the
situation.
Polymorphism exists in three
distinct forms in Jav
• Method overloading
• Method overriding through inheritance
• Method overriding through the Java interface
What is explicit casting?
Explicit casting in the process
in which the complier are specifically informed to about transforming the
object.
Example
long i =
700.20;
int j = (int)
i; //Explicit casting
What is the Java Virtual Machine (JVM)?
The Java Virtual Machine is software that can be ported onto
various hardware-based platforms
What do you understand by downcasting?
The process of Downcasting refers to the
casting from a general to a more specific type, i.e. casting down the hierarchy
What are Java Access Specifiers?
Or What is the
difference between public, private, protected and default Access Specifiers? Or What are different types of access modifiers?
Access specifiers are keywords that
determine the type of access to the member of a class. These keywords are for
allowing
privileges to parts of a program such as functions and variables. These are:
• Public
: accessible to all classes
• Protected
: accessible to the classes within the same package and any subclasses.
• Private : accessible only to the class
to which they belong
• Default
: accessible to the class to which they belong and to subclasses
within the same package
Which class is the superclass of every
class?
Object.
Name primitive Java types.
The 8 primitive types are byte, char, short, int,
long, float, double, and boolean.
What is the difference between static and non-static variables?
Or
What are class variables?
Or
What is static in java?
Or
What is a static method?
A static variable is associated with the class as a whole rather
than with specific instances of a class. Each object will share a common copy
of the static variables i.e. there is only one copy per class, no matter how
many objects are created from it. Class variables or static variables are
declared with the static keyword in a class. These are declared outside a class
and stored in static memory. Class variables are mostly used for constants.
Static variables are always called by the class name. This variable is created
when the program starts and gets destroyed when the programs stops. The scope
of the class variable is same an instance variable. Its initial value is same
as instance variable and gets a default value when its
not initialized corresponding to the data type. Similarly, a static method is a
method that belongs to the class rather than any object of the class and
doesn’t apply to an object or even require that any objects of the class have
been instantiated.
Static methods are implicitly final, because overriding is done based on the
type of the object, and static methods are attached to a class, not an object.
A static method in a superclass can be shadowed by
another static method in a subclass, as long as the original method was not declared
final. However, you can’t override a static method with a non-static method. In
other words, you can’t change a static method into an instance method in a
subclass.
Non-static variables take on unique values with each object
instance.
What is the difference between the boolean & operator and the && operator?
If an expression involving the boolean & operator is evaluated, both operands
are evaluated, whereas the && operator is a short cut operator. When an
expression involving the && operator is evaluated, the first operand is
evaluated. If the first operand returns a value of true then the second operand
is evaluated. If the first operand evaluates to false, the evaluation of the
second operand is skipped.
How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the
size of the type allowed by the operation.
What if I write static public void instead of public static
void?
Program compiles and runs properly.
What is the difference between declaring a variable and defining
a variable?
In declaration we only mention the type of the variable and its
name without initializing it. Defining means declaration + initialization. E.g.
String s; is just a declaration while String s = new String (”bob”); Or String
s = “bob”; are both definitions.
What type of parameter passing does Java support?
In Java the arguments (primitives and objects) are always passed
by value. With objects, the object reference itself is passed by value and so
both the original reference and parameter copy both refer to the same object.
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