Environment variables : What it is? How to set it?

Java Bean

What is Java Bean?

Java bean is a simple java class with instance variables (all private) and each instance variable having getter and setter methods (public) for them.

Example :

 class Person {  
 private int id;  
 private String name;  
 private String address;  
 public int getId () { return id; }  
 public String getName () { return name; }  
 public String getAddress () { return address; }  
 public void setId (int id) { this.id = id; }  
 public void setName (String name) { this.name = name; }  
 public void setAddress (String address) { this.address = address; }  
 }  

Java and its Features in brief

What is Java?

Java is a Object Oriented Programming Language.
Main Features of Java are :
Class :- Template
Object :- Instance with Specific Values
Inheritance :- Creating new classes by extending the features of existing classes
Polymorphism :- A single variable of class type can take multiple forms i.e. a variable can be assigned to objects of different types along the class hierarchy

Class :

Definition of class
class <name>
{
variables;
constructors;
methods;
}

class X{
//variables
int x;
//constructors
X(int x) { this.x = x; } 
//methods
int getX() { //body }
void setX(int x) { //body}
}

Object :

Using keyword new we create an instance i.e. object of a class.
X temp = new X(5);

Inheritance :

Another class  Y
Class Y extends X{
//variables
int y;
//constructors
Y(int x,int y) { super(x); this.y = y; } 
//methods
int getY() { //body }
void setY(int y) { //body}
}

Here the method getX() and setX(int x) are inherited in class Y and can be called from class Y.

Polymorphism :

Another class Z instatiates X and Y classes.
class Z{
int z;
p.s.v.m.(){
X temp = new X(5);
System.out.println("X : " + temp.getX());
temp = new Y(5,10);
System.out.println("X : " + temp.getX()); // cannot call temp.getY() as temp is variable of type X which does
                                                              // not have method getY()
}
}
Same variable can take multiple forms i.e. it can be assigned an instance of X or Y. Hence same variable temp takes multiple forms.
This is polymorphism.

How to implement singleton class in java?

Hello All,

Hope you will enjoy this article.

How to implement singleton class in java?

Concept of Singleton : Singleton class is one for which only one instance i.e. object of it will be created.

To achieve this requirement it is important create first time the object for the class but afterwards whenever there is need for instance of that class .. reference for already created instance should be returned.

Following code will serve as an example for singleton class :

public class Singleton {

private static Singleton;
protected Singleton()                   //protected constructor
{
}

public static getInstance(){
{
           if(Singleton == null)
                      Singleton = new Singleton();
           return Singleton;
}
}

Java Code to find second highest number in an array in java

Hi ,

Please find below the code to find second highest number in an array in java.

Method 1:
public class SecondHighestNumber {

public static void main(String[] args) {

int [] arr = { 1,19,9,7,5,2,3,4,16,12};

int firstHighest , secondHighest , i;

if(arr[0] > arr[1])
{
            firstHighest = arr[0];
            secondHighest = arr[1];
}
else
{
            firstHighest = arr[1];
            secondHighest = arr[0];

}

for(i=2;i<arr.length();i++)
{
           if(arr[i] >= firstHighest)
           {
             secondHighest = firstHighest;
             firstHighest = arr[i];
           }
           else if(arr[i]>secondHighest)
           {
            secondHighest = arr[i];
           }
}

System.out.println(" The Second highest number in an array is "+secondHighest);

}

}

How to implement tree in java?

Steps
1. Create class Node with generic parameter T and having instance variables as
     1.1 data of type T i.e. T data;
     1.2 List of Node of Type T i.e. List<Node<T>> children;
     1.3 parent of type Node<T> i.e. Node<T> parent;
   & methods as
     Constuctors as
      public Node(T data)
     {
            this.data = data;
      }
      public Node(T data,Node<T> parent)
      {
           this.data = data;
           this.parent = parent;
       }
       Add methods to getChildren, addChild, setParent.
2. Create class Tree with instance variables as
     2.1 root with type Node<T> i.e. Node<T>root;
3. Create Class TestTree with main method.
    Create a local variable t of type Tree.
    Add root and other nodes inside the tree.

Thanks,
Sagar

Java Interview Questions

Interview Question 1.
How to find first non repeated character in the String( Write Java Code)