InstanceOfJava

Basic java programs

Posted by: Instanceofjava Posted date: 11:14 AM / comment : 0 Core java Interview Questions , java interview programs

Super keyword interview questions java

Posted by: Instanceofjava Posted date: 10:43 PM / comment : 0 Concept and Interview Questions , java programming interview questions

Super Keyword:

The functionality of super keyword is only to point the immediate super class object of the current object.
super keyword is applicable only in the non static methods and super keyword not applicable in the static methods.
super keyword used to access the members of the super class object.
super.member;
It is used to store super class non static members memory reference through current sub class object for separating super class members from subclass members.
We can call super class constructor in sub class using super() call.
We can access super class methods and variables in sub class using super.variable_name, super.method();

Uses of super :

1. By using super keyword we can access super class variables in sub class.

Using super keyword we can access super class variables from sub class.
super.variable_name.

package com.superkeywordinjava;
public Class SuperDemo{
int a,b;
}

package com.superkeywordinjava;
public Class Subdemo extends SuperDemo{
int a,b;
void disply(){
System.out.println(a);
System.out.println(b);
super.a=10;
super.b=20;
System.out.println(super.a);
System.out.println(super.b);
}
public static void main (String args[]) {
Subdemo obj= new Subdemo();
obj.a=1;
obj.b=2;
obj.disply();
}
}

Output:

2. By using super keyword we can access super class methods in sub class.

Using super keyword we can call super class methods from sub class.
super.method();.

package com.instanceofjavaforus;
public Class SuperDemo{
int a,b;
public void show() {
System.out.println(a);
System.out.println(b);
}
}

package com.instanceofjavaforus;
public Class Subdemo extends SuperDemo{
int a,b;
void disply(){
System.out.println(a);
System.out.println(b);
super.a=10;
super.b=20;
super.show();
}
public static void main (String args[]) {
Subdemo obj= new Subdemo();
obj.a=1;
obj.b=2;
obj.disply();
}
}

Output:

3. We can call super class constructor from class constructor:

By using super keyword we can able to call super class constructor from sub class constructor.
Using super();
For the super(); call must be first statement in sub class constructor.

package com.superinterviewprograms;
public Class SuperDemo{
int a,b;
SuperDemo(int x, int y){
a=x;
b=y
System.out.println("Super class constructor called ");
}
}

package com.superinterviewprograms;
public Class Subdemo extends SuperDemo{
int a,b;
SubDemo(int x, int y){
super(10,20);
a=x;
b=y
System.out.println("Sub class constructor called ");
}
public static void main (String args[]) {
Subdemo obj= new Subdemo(1,2);
}
}

Output:

Super class constructor called
Sub class constructor called

key points:

Super(); call must be first statement inside constructor.
By default in every class constructor JVM adds super(); call in side the constructor as first statement which calls default constructor of super class, if we are not not calling it.
If we want to call explicitly we can call at that time default call wont be there.

4.What will happen if we are calling super() in constructor but our class does not extending any class?

if our class not extending any class Yes still we can use super(); call in our class
Because in java every class will extend Object class by default this will be added by JVM.
But make sure we are using only super(); default call we can not place parameterized super call because Object class does not have any parameterized constructor.

package com.superinterviewprograms;
public Class Sample{
Sample(){
super();
System.out.println("Sample class constructor called ");
}
public static void main (String args[]) {
Sample obj= new Sample();
}
}

Output:

Sample class constructor called

5.What if there is a chain of extended classes and 'super' keyword is used

package com.superinterviewprograms;
public Class A{
A(){
System.out.println("A class constructor called ");
}
}

package com.superinterviewprograms;
public Class B extends A{
B(){
System.out.println("B class constructor called ");
}
}

package com.superinterviewprograms;
public Class C extends B{
C(){
System.out.println("C class constructor called ");
}
public static void main (String args[]) {
C obj= new C();
}
}

Output:

A class constructor called
B class constructor called
C class constructor called

6. Can we call super class methods from static methods of sub class?

No we can not use super in static methods of sub class Because super belongs to object level so we can not use super in static methods.
If we try to use in sub class static methods compile time error will come.

super keyword in java interview example program frehser

Data types in java with example programs

Posted by: Instanceofjava Posted date: 7:36 PM / comment : 0 Concept and Interview Questions , Core java Interview Questions

The data type is something which gives information about
Size of the memory location and range of the data that can be accommodated inside that location.
Possible legal operations those can be performed on that location.
What type of result come out from an expression when we use these types inside that expression.
Whichever the keyword gives these semantics is treated as "data type".
The java language provides different categories of data types.

1.Primitives Data types:

The primitive data types are the predefined data types given by the programming language and they are meant for storing a single value.
Based on the type and range of data, primitive types are divided into 8 types.

1.Integer category:

This category can be used for storing numbers which can be either positive value or negative value without decimal points.
In this category we have 4 primitive data types whose memory sizes are different.
All the 4 types under this category are used for storing same data. But there ranges are different. The java language is providing 4 types under Integer category. So that the memory is utilized efficiently.

byte
short
int
long

byte data type in java:

Size 1 byte. i.e 8 bits
Minimum value is -128 (-2^7)
Maximum value is 127 (2^7 -1)
Default value is 0

Java example program on byte data type:

package com.instanceofjava;
Class ByteDemo {
public static void main(String[] args) {
byte x=10;
byte y=20;
byte z= (byte) (x+y);
System.out.println(z);
}
}

Output:

short data type in java:

Size 2 bytes.
Minimum value is -32,768 (-2^15)
Maximum value is 32,767 (2^15-1)
Default value is 0

Java example program on short data type:

package com.instanceofjava;
Class ShortDemo {
public static void main(String[] args) {
short x=10;
short y=20;
short z= (short) (x+y);
System.out.println(z);
}
}

Output:

int data type in java:

Size 4 bytes.
Minimum value is - 2,147,483,648.(-2^31)
Maximum value is 2,147,483,647 (2^31 -1)
Default value is 0

Java example program on int data type:

package com.instanceofjava;
Class IntDemo {
public static void main(String[] args) {
int x=10;
int y=20;
int z=x+y;
System.out.println(z);
}
}

Output:

long data type in java:

Size 8 bytes.
Minimum value is -9,223,372,036,854,775,808.(-2^63)
Maximum value is 9,223,372,036,854,775,807 (2^63 -1)
Default value is 0

Java example program on long data type:

package com.instanceofjava;
Class LongDemo {
public static void main(String[] args) {
long x=109876677777l;
long y=20666677766l;
long z=x+y;
System.out.println(z);
}
}

Output:

130543355543

2.Floating point category:

This category can be used for storing numbers which can be either +VE or –VE with decimal point. In the floating point category we have two types whose size is different. The two data types are float and double.
Both the data types under the floating point category are used for storing same data but there range is different. The java language provide as two data types under floating point category so that memory is utilized efficiently.
Default value of float is 0
Default value of double is 0.0

float
double

float data type in java:

Size 4 bytes.
Minimum value is 1.4e-45
Maximum value is 3.4e38
Default value is 0.0f

Java example program on float data type:

package com.instanceofjava;
Class FloatDemo {
public static void main(String[] args) {
float x=231231.0031f;
float y= 53423423434.43231f;
float z= x+y;
System.out.println(z);
}
}

Output:

5.3423653E10

double data type in java:

Size 8 bytes.
Minimum value is 4.9e-324
Maximum value is 1.8e308
Default value is 0.0d

Java example program on double data type:

package com.instanceofjava;
Class DoubleDemo {
public static void main(String[] args) {
double x=231231.0031f;
double y= 53423423434.43231f;
double z= x+y;
System.out.println(z);
}
}

Output:

5.342365466543541E10

3.Character category:

This category can be used for storing a single character. A character can be represented by alphabets, a digit and special symbols.
This category contains only one data type an it is char.
Default value of char is "one space"

char

char data type in java:

Size 2 bytes.
Minimum value is 0
Maximum value is 65,535
Default value is ' '

Java example program on char data type:

package com.instanceofjava;
Class CharDemo {
public static void main(String[] args) {
char a='a';
System.out.println(a);
}
}

Output:

4.Boolean category:

This category can be used for storing either true or false. Under the Boolean category only one data type an it is Boolean. The size is dependent on JVM to JVM.

boolean data type in java:

boolean data type represents one bit of information.
There are only two possible values: true and false.
This data type is used for simple flags that track true/false conditions.
Default value is false. '

Java example program on boolean data type:

package com.instanceofjava;
Class BooleanDemo {
public static void main(String[] args) {
boolean x = false;
System.out.println(x);
}
}

Output:

false

Top 10 interview questions on java interfaces

Posted by: Instanceofjava Posted date: 7:49 PM / comment : 7 Concept and Interview Questions , Core java Interview Questions , java programming interview questions

1.What is an interface in Java.

Before Java 8 interfaces are pure abstract classes which allow us to define public static final variables and public abstract methods(by default).
In java 8 introduced static methods and default methods in interfaces.
Java 8 Interface Static and Default Methods
We can develop interfaces by using "interface" keyword.
A class will implements all the methods in an interface.

package com.instanceofjava;
interface JavaInterface{
int x=12;
void show();
}

package com.instanceofjava;
Class A implements JavaInterface {
void show(){
// code
}
}

package com.instanceofjava;
interface Java8Interface{
int x=12;
void show();
default void display(){
System.out.println("default method of interface");
}
Static void print(String str){
System.out.println("Static method of interface:"+str);
}
}

2.What will happen if we define a concrete method in an interface?

By default interface methods are abstract.
if we declare any concrete method in an interface compile time error will come.
Error:Abstract methods do not specify a body

3.Can we create non static variables in an interface?

No.We can not create non static variables in an interface.
If we try to create non static variables compile time error comes.
By default members will be treated as public static final variables so it expects some value to be initialized.

package com.instanceofjava;
interface JavaInterface{
int x, y; // compile time error
}

4.What will happen if we not initialize variables in an interface.

Compile time error will come because by default members will be treated as public static final variables so it expects some value to be initialized.

package com.instanceofjava;
interface JavaInterface{
int x, y; // compile time error: The blank final field y may not have been initialized
}

5.Can we declare interface members as private or protected?

package com.instanceofjava;
interface JavaInterface{
private int x; // compile time error: Illegal modifier for the interface field Sample.x; only
public, static & final are permitted
protected int a; // compile time error: Illegal modifier for the interface field Sample.a; only
public, static & final are permitted
}

7.When we need to use extends and implements?

A class will implements an interface.
A class will extends another class.
An interface extends another interface.

6.Can we create object for an interface?

NO. We can not create object for interface.
We can create a variable fro an interface

package com.instanceofjava;
interface JavaInterface{
void show();
}

package com.instanceofjava;
interface A implements JavaInterface {
void show(){
// code
}
public static void main(String args[]){
JavaInterface obj= new JavaInterface(); // Error: Cannot instantiate the type JavaInterface
}
}

7.Can we declare interface as final?

No. Compile time error will come.
Error: Illegal modifier for the interface Sample; only public & abstract are permitted

8.Can we declare constructor inside an interface?

No. Interfaces does not allow constructors.
The variables inside interfaces are static final variables means constants and we can not create object fro interface so there is no need of constructor in interface that is the reason interface doesn't allow us to create constructor.

9.What will happen if we are not implementing all the methods of an interface in class which implements an interface?

A class which implements an interface should implement all the methods (abstract) otherwise compiler will throw an error.
The type Example must implement the inherited abstract method JavaInterface.show()
If we declare class as abstract no need to implement methods.
No need of overriding default and static methods.

package com.instanceofjava;
interface JavaInterface{
void show();

}

package com.instanceofjava;
interface A implements JavaInterface { // The type Example must implement the inherited
abstract method JavaInterface.show()
public static void main(String args[]){
}
}

10.How can we access same variables defined in two interfaces implemented by a class?

By Using corresponding interface.variable_name we can access variables of corresponding interfaces.

11.If Same method is defined in two interfaces can we override this method in class implementing these interfaces.

Yes implementing the method once is enough in class.
A class cannot implement two interfaces that have methods with same name but different return type.

Hibernate configuration file

Posted by: Instanceofjava Posted date: 4:59 PM / comment : 0 hibernate , hibernate interview questions

1.hibernate.dialect:

This property hibernate.dialect makes Hibernate generate the appropriate SQL for the given database.

2.hibernate.connection.driver_class:

This property hibernate.connection.driver_class specifies jdbc driver class name

3.hibernate.connection.username:

This property hibernate.connection.username specifies database user name.

4.hibernate.connection.password:

This property hibernate.connection.password specifies password.

hibernate.cfg.xml file structure

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration SYSTEM
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.driver_class">Driver Class Name </property>
<property name="connection.url">URL </property>
<property name="connection.user">user name</property>
<property name="connection.password">password</property>
<property name="show_sql">true/false</property>
<property name="dialet">Database dialet class</property>
<property name="hbm2ddl.auto">create/update or what ever</property>
<property name="hibernate.jdbc.batch_size">hibernate container that every N rows to be
inserted as batch.</property>
<mapping resource="hbm file 1 name .xml" />
<mapping resource="hbm file 2 name .xml" />
</session-factory>
</hibernate-configuration>

Example hibernate.cfg.xml. file for mysql

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration SYSTEM
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration><session-factory>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url"> jdbc:mysql://localhost/test</property>
<property name="connection.user">user </property>
<property name="connection.password">password</property>
<property name="show_sql">true/false</property>
<property name="dialet">org.hibernate.dialect.MySQLDialect</property>
<property name="hbm2ddl.auto">create</property>
<property name="hibernate.jdbc.batch_size">50</property>
<mapping resource="hbm_file1.xml" />
<mapping resource="hbm_file2.xml" />
</session-factory>
</hibernate-configuration>

Example hibernate.cfg.xml. file for oracle Db

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration SYSTEM
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration><session-factory>
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url"> jdbc:oracle:thin:@localhost:1521:xe</property>
<property name="connection.user">user </property>
<property name="connection.password">password</property>
<property name="show_sql">true/false</property>
<property name="dialet">org.hibernate.dialect.Oracle9Dialect</property>
<property name="hbm2ddl.auto">create</property>
<property name="hibernate.jdbc.batch_size">50</property>
<mapping resource="hbm_file1.xml" />
<mapping resource="hbm_file2.xml" />
</session-factory>
</hibernate-configuration>

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Basic java programs

Top 10 Java interview questions on final keyword

Super keyword interview questions java

Super Keyword:

Data types in java with example programs

1.Primitives Data types:

1.Integer category:

2.Floating point category:

3.Character category:

4.Boolean category:

Top 10 interview questions on java interfaces

Hibernate configuration file