JAVA: Implementing ArrayList in JAVA - Simple program

package Programs;

import java.util.Arrays;

public class implementingArrayList {

 int get[] = new int[10];
 int size;

 public void add(int x) {
  if (size != 0) {
   if (size % 10 == 0) {

    get = Arrays.copyOf(get, (get.length + 10));

   }
  }
  get[size] = x;
  ++size;
 }

 public void remove(int x) {

  for (int i = 0; i < get.length; i++) {
   if (get[i] == x) {
    for (int j = (i + 1); j < (get.length - 1); j++) {
     get[i] = get[j];
     i++;
    }

    size--;
    get = Arrays.copyOf(get, get.length - 1);
    break;
   }
  }

 }

 public static void main(String args[]) {
  implementingArrayList list = new implementingArrayList();
  list.add(1);
  list.add(2);
  list.add(3);
  list.add(4);
  list.add(5);
  list.add(11);
  list.add(12);
  list.add(13);
  list.add(14);
  list.add(15);
  list.add(21);
  list.add(22);
  list.add(23);
  list.add(24);
  list.add(25);
  list.add(100);
  list.remove(14);
  System.out.println("Size of the list is" + list.size);
  for (int x = 0; x < list.size; x++) {
   System.out.println(list.get[x]);
  }
 }

}

JAVA: Reading integer from the keyboard without using Integer.ParseInt() method

import java.io.*;

public class readIntegerWithoutUsingParseint {

    public static void main(String args[]) throws IOException{
         BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
         String integer = input.readLine();
         char ar[]= integer.toCharArray();
         int x = (int)'0';
         int sum = 1;
         int number=0;
         
         for(int i=(ar.length-1); i>=0; i--){
         number = number + (sum)*((int)ar[i]-x);
         sum = sum*10;
         }

         System.out.println(number);

    }
}

JAVA: Check the number if its perfect square or not.

import java.util.*;
import java.io.*;
public class perfectSquare {

    public static void main(String args[]) throws NumberFormatException, IOException{
       
        BufferedReader as = new BufferedReader(new InputStreamReader(System.in));
        int x = Integer.parseInt(as.readLine());
        boolean y = true;
    //124System.out.println(x);
        for(int i=0; i<=x/2; i++){
            if(i*i <= x){
            if(x == (i*i)){
                System.out.println(x+ " is a perfect square");
                y = false;
                break;
               
            }
            }
        }
       
        if(y == true){
            System.out.println(x+ " is not a perfect square");   
           
        }
       
    }
   
}

JAVA: Removing White Spaces from the String without using inbuilt String functions Like ReplaceAll(), Trim(), Split().

Below is the code.
package Strings;

public class removingwhitespaceWithoutFunctions {
    public static void main(String args[]){
        String x = "  aslam anweranwer      hello hi we hello a  ";
        int y = x.length();
        char c[]= x.toCharArray();
        char h[] ;
        int j=0,t=0;
        for(int i=0;i<y;i++){
            int m = c[i];
        if(m ==32){       // we can compare space also, here i am comparing the asccii code.
            ++t;                // count how many spaces are there.
}
        }
        h = new char[y - t]; // set the length of the array which is going to hold the new string.
        System.out.println(h.length);
        for(int i=0;i<y;i++){
            int m = c[i];
        if(m !=32){
   
        h[j]=c[i];   
        j=j+1;   
        }
        }
       
    System.out.println(h);
        }}

JAVA: MultiThreading Producer and Consumer.

Producer and Consumer in the same program.(Single person doing multitask ,with one hand produce and with another hand  consume)

The below program has two methods one is Producer() and other one is Consumer().
Producer thread is main thread and Consumer thread is child thread.

//Begin Program
package Programs;

public class producerConsumer implements Runnable {
    static   int x;
    static boolean y,produced = false;
    public void Producer() throws InterruptedException{
        synchronized(this){
            Thread t2 = new Thread(this);
            t2.start();
        for(int i=0;i<10 data-blogger-escaped-0="" data-blogger-escaped-1="" data-blogger-escaped-2="" data-blogger-escaped-3="" data-blogger-escaped-4="" data-blogger-escaped-5="" data-blogger-escaped-6="" data-blogger-escaped-7="" data-blogger-escaped-8="" data-blogger-escaped-9="" data-blogger-escaped-args="" data-blogger-escaped-as.producer="" data-blogger-escaped-as="new" data-blogger-escaped-catch="" data-blogger-escaped-child="" data-blogger-escaped-consumed="" data-blogger-escaped-consumer="" data-blogger-escaped-e.printstacktrace="" data-blogger-escaped-e="" data-blogger-escaped-false="" data-blogger-escaped-for="" data-blogger-escaped-hread="" data-blogger-escaped-i="" data-blogger-escaped-int="" data-blogger-escaped-interruptedexception="" data-blogger-escaped-main="" data-blogger-escaped-nd="" data-blogger-escaped-notifyall="" data-blogger-escaped-nterruptedexception="" data-blogger-escaped-onsumed="" data-blogger-escaped-out="" data-blogger-escaped-pre="" data-blogger-escaped-produced="" data-blogger-escaped-producerconsumer="" data-blogger-escaped-program="" data-blogger-escaped-public="" data-blogger-escaped-put:="" data-blogger-escaped-roduced="" data-blogger-escaped-run="" data-blogger-escaped-static="" data-blogger-escaped-synchronized="" data-blogger-escaped-system.out.println="" data-blogger-escaped-this.consumer="" data-blogger-escaped-this.notifyall="" data-blogger-escaped-this.wait="" data-blogger-escaped-this="" data-blogger-escaped-thread="" data-blogger-escaped-throws="" data-blogger-escaped-tring="" data-blogger-escaped-try="" data-blogger-escaped-void="" data-blogger-escaped-while="" data-blogger-escaped-x="" data-blogger-escaped-y="true;">

JAVA: Why Strings are immutable in JAVA

First lets have the definition of the Immutability
Immutability of an object is that the state of an object(hashcode content) cannot be changed once its created.

Let me show you one example which is mutable.
Consider the class StringBuilder.

StringBuilder sb = new StringBuilder("asla");
        System.out.println(sb.hashCode());                // out put : 817639612
        System.out.println(sb);                                   //asla
        sb.append("m");
        System.out.println(sb.hashCode());                 // out put : 817639612
        System.out.println(sb);                                   // aslama
        sb.append("an");
        System.out.println(sb.hashCode());                  // out put : 817639612
        System.out.println(sb);                                     //aslaman


In the above example you can see the same hashcode is being overriden with different values thats why the object sb is mutable in the above example.


Now lets consider strings.   
        String x ="IBM";
        System.out.println(x.hashCode());       //72276
         x = x+"india";
        System.out.println(x.hashCode());       //-873372829

now the same object x has different hashcode when its concatenated. what happened to the value which is there in 72276?
Its still there . So string object state once created cannot be changed , hence strings are immutable.

 Why
Strings have concept called string pooling.
String x = "IBM"
String y = "IBM"

In the above example only one object is created x and string y has the same reference as that of x .
This is the benefit of having String pooling. So Strings with same value will have only one object.

Now if we change the value of x say x = x+ "INDIA";
JVM cannot allocate the value of the x as IBMINDIA in the same reference which its pointing because y's value is IBM , you cannot make it IBMINDIA. Hence the reference which is having the value IBM will be there and cannot be changed as strings are immutable . JVM Will create new reference for x with the value IBMINDIA and x will be pointing to that.


Now its clear that why strings are immutable.

There are other reasons as well I have just discussed the main reason for Strings immutability.