What is encapsulation?

Encapsulation :  It is a process by which wrapping code and data into a single unit.

Example : A java bean is a best example of heighly encapsulated class where any instance variable declared as private and these private variable can access through public method.

package com.pky.com;  
public class Employee{  
private String name;  
   
public String getName(){  
return name;  
}  
public void setName(String name){  
this.name=name  
}  
}  


//save as EmpTest.java  
package com.pky.com;  
class EmpTest{  
public static void main(String[] args){  
Employee e=new Employee();  
e.setName("Pradeep Yadav");  
System.out.println(s.getName());  
}  
}

Output :
Pradeep Yadav

Advantage of Encapsulation :

* you can make the class read-only or write-only.

*  you can control over the data

Using yield() and join() in threading in java

Use of yield() : yield() is used in threading to allow another thread to execute which have same priority and itself switch running to runnable state.

Example :

package mypkg;

public class YieldDemo {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Thread p = new Producer();
Thread c = new Consumer();
p.setPriority(Thread.MIN_PRIORITY);
c.setPriority(Thread.MAX_PRIORITY);
p.start();
c.start();
}
}

class Producer extends Thread {
public void run() {
for (int i = 0; i < 5; i++) {
System.out.println("I am producer :" + i);
Thread.yield();
}
}
}

class Consumer extends Thread {
public void run() {
for (int i = 0; i < 5; i++) {

System.out.println("I am consumer :" + i);
Thread.yield();
}
}


}

Use of join() : This method is used to current thread execute completely without any intrrupt. When it execute completely then control give other thread for execution.

Example :

Fetch any number of heighest salary from table in mysql

You can fetch any number of heighest salary from table in mysql using following query -

select * from emp order by salary desc limit 0,1;

In above query emp is a table, salary is a column so when we change limit value like 0 or 1 or 2 it will be fetch heighest, second heighest, and third heighest and so on. Each red color word is a keword in mysql.

How to delete duplicate value from table in mysql?

Here is a siple query to delete duplicate value from table :

DELETE e1 FROM employee e1, employee e2 WHERE e1.name = e2.name AND e1.id > e2.id;

Print diamond shape with java code

package example;

/**
 *
 * @author pradeep
 */
public class DiamondDemo {

    public static void main(String[] args) {
        int n = 5;
        for (int i = 0; i <= n; i++) {
            for (int j = 0; j <= n - i; j++) {
                System.out.print(" ");
            }
            for (int j = 0; j <= i; j++) {
                System.out.print("*");
            }
            for (int j = 0; j < i; j++) {
                System.out.print("*");
            }
            System.out.println();
        }
        for (int i = 0; i < n - 1; i++) {
            for (int j = 0; j <= i; j++) {
                System.out.print(" ");
            }
            for (int j = 0; j <= n - i; j++) {
                System.out.print("*");
            }
            for (int j = 0; j < n - i; j++) {
                System.out.print("*");
            }
            System.out.println();
        }

    }
}

How to override compareTo() of Comparable interface

Its very simple just implements camparable interface in one class with private varible and there setter and getter and override compareTo() method. After that create another public class with main() and create previous class's object and set values. You can understand with following code :-


package example;

import java.util.*;

/**
 *
 * @author pradeep
 */
public class ComparableDemo {

    public static void main(String args[]) {
        User u = new User();
        u.setName("pradeep");
        User u1 = new User();
        u1.setName("Ajeet");
        User u2 = new User();
        u2.setName("sameer");
        List<User> list = new ArrayList<User>();
        list.add(u);
        list.add(u1);
        list.add(u2);
        Collections.sort(list);
        for (User user : list) {
            System.out.println(user.getName());
        }
    }
}

class User implements Comparable<User> {

    private String name;

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int compareTo(User n) {
        if (this.getName().compareTo(n.getName()) > 0) {
            return 1;
        }
        if (this.getName().compareTo(n.getName()) < 0) {
            return -1;
        }
        return 0;
    }
}