InstanceOfJava

Creating array of objects in java example program

Posted by: Instanceofjava Posted date: 12:13 PM / comment : 0 Core java Interview Questions , java programming interview questions , Java Programs

Array is collection of similar data types.
Arrays can hold collection of data with indexes
We already know that we can hold group of primitive variables
Arrays can hold referenced variables also like Strings and objects
So we can say it is possible to store or create array of objects in java

Declaring arrays in java:

One dimensional array can be created like
int[] singlearray;
Two dimensional array can be created like
int[][] intdoubleArray;
double[][] doubleArray;

Instantiation and Initialization of Arrays

Program #1: Java example program to store string object in array

package arraysofobjectsinjava;
public class ArrayOfObjects {
/**
* @www.instanceofjava.com
* creating and assigning values to arrays in java
*/
public static void main(String[] args) {
int[] a= new int[2];
a[0]=1;
a[1]=2;
System.out.println(a[0]);
System.out.println(a[1]);
int[] var= {1,2,3,4,5};
for (int i = 0; i < var.length; i++) {
System.out.println(var[i]);
}
int[][] array=new int[2][2];
array[0][0]=1;
array[0][1]=2;
array[1][0]=3;
array[1][1]=4;
for(int i=0; i<array.length; i++) {
for(int j=0; j<array[1].length; j++)
System.out.print(array[i][j] + " ");
System.out.println();
}
}
}

Output:

Array of objects in java:

Program #2: Java example program to store string object in array

package arraysofobjectsinjava;
public class ArrayofStringObjects {
/**
* @www.instanceofjava.com
* Storing String objects in String array
*/
public static void main(String[] args) {
String a[]= new String[5];
a[0]="array of objects";
a[1]="object array in java";
a[2]="array of objects in java example program";
a[3]="array of objects in java tutorial";
a[4]="how to make array of objects in java";
for (int i = 0; i < a.length; i++) {
System.out.println(a[i]);
}
}
}

Output:

array of objects
object array in java
array of objects in java example program
array of objects in java tutorial
how to make array of objects in java

Creating custom array of objects in java

We can also store custom objects in arrays .
Create a employee class.
Create multiple objects of employee class and assign employee objects to array.
Arrays can store objects but we need to instantiate each and every object and array can store it

Program#3: java example program to create custom objects and store in array

Employee.java

package arraysofobjectsinjava;
public class Employee {
String name;
int id;
Employee(String name, int id){
this.name=name;
this.id=id;
}
}

Tower of hanoi recursive solution using Java

Posted by: Instanceofjava Posted date: 10:32 AM / comment : 0 Core java Interview Questions , java programming interview questions , Java Programs

Towers of Hanoi is a famous game.
In this game there are three poles and N number of disks placed one over another in increasing in size from top to bottom.

Objective of this game is to move disks from first pole to last pole.
And the condition is we can not place bigger disk on top of smaller disk.
Initially all disks placed in first pole smaller disk will be on top and bigger disk will be on bottom.
We need to move all the disks from from first pole to last pole.

Rules of tower of Hanoi:

We can move only one disk at a time.
At any poi of time larger disk can not be placed on smaller disk.

In order to solve this problem we have given a second pole so we can use second pole and move disks from first pole to third pole.
We can solve this using rec recursive procedure.

Tower of Hanoi with Single disk: N=1

Three poles are A , B ,C
And a disk is present at A we need to move from A to C
As it its single disk we can directly move disk A - > C

Tower of Hanoi with Two disks : N=2

Three poles are A , B ,C
And two disks are placed in pole A, Disk 1 and Disk2 top to bottom.( assume Disk 2 is smaller and Disk 1 bigger)
Move Disk2 from A to B
Move Disk1 From A to C.
Move Disk2 from B to C.

tower of hanoi in data structure program

Tower of Hanoi with Three disks : N=3

Three poles are A , B ,C
And three disks are placed in pole A, Disk 1 top to bot, Disk2 and Disk 2 top bottom to .( assume Disk 3 is smaller and Disk 1 bigger)
In this firs we need to move two disk from A to B which we already done in above procedure
So we need to repeat that here.
Move Disk1 from A to C.
Now Moving two disks from B to C we have already seen in above procedure so its recursive.

Tower of Hanoi Recursive Algorithm:

N = number of disks

If N == 1

Move Single disk from A to C

If N >1

1.Move n-1 disks from start A to B TowersofHanoi(n-1,start, end , aux)
Move last Disk from A to C
Move n-1 disks from B to C. TowersofHanoi(n-1,start, aux, end )

Step 1 and 3 are recursive procedures.
Lets see hoe to write java recursive program for this towers of Hanoi problem
Here B as auxiliary pole.

Program #1: Java Example program on towers of Hanoi:

package towersofhanoi;
import java.util.Scanner;
public class TowersofHanoi {
public void TOH(int n, String start, String aux, String end) {
if (n == 1) {
System.out.println(start + " -> " + end);
} else {
TOH(n - 1, start, end, aux);
System.out.println(start + " -> " + end);
TOH(n - 1, aux, start, end);
}
}
public static void main(String[] args) {
TowersofHanoi towersOfHanoi = new TowersofHanoi();
System.out.print("Enter number of discs: ");
Scanner scanner = new Scanner(System.in);
int discs = scanner.nextInt();
towersOfHanoi.TOH(discs, "A", "B", "C");
}
}

Output:

Enter number of discs:
3
A -> C
A -> B
C -> B
A -> C
B -> A
B -> C
A -> C

8 different ways to convert int to String in java

Posted by: Instanceofjava Posted date: 9:48 PM / comment : 0 Core java Interview Questions , java programming interview questions

How to convert string to int or integer to string in java?
When we are working on a project we will be having some scenarios of expecting a string from int or integer from string.
Now we will be discussing on how to convert Integer to String in java with example java programs.

8 different ways to convert int to String in java

1.Convert Integer to String using Integer.toString() method:
2.Convert Integer to String using String.valueOf() method.
3.Convert Integer to String / int to String using new Integer(int).toString()
4.Convert Integer to String / int to String using String.format() method
5.Convert Integer to String / int to String using DecimalFormat
6.Convert Integer to String/ int to String using StringBuffer / StringBuilder
7.Convert Integer to String / int to String directly by adding to ""
8.Convert Integer to String / int to String using Special radix.

1.Convert Integer to String using Integer.toString() method:

Integer is a wrapper class in java which is mainly used to represent or convert primitive int value to object.
And Integer class having some predefined methods.
Integer class has special predefined method to convert integer value to string toString();
toString is a static method in Integer class so that by using class name itself we can call that method to convert Integer to corresponding string value.

Program #1: Java Example program to convert Integer to String by using toString() method:

Output:

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
Integer i = new Integer(64);
//converting integer to string by calling toString() method on integer object
String str= i.toString();
// also we can use like String str= Integer.toString(i);
System.out.println(str);
}
}

Output:

2.Convert Integer to String using String.valueOf() method.

Integer class have toString() method to convert integer to string value same way String class also has valueOf() method to convert int or integer to string.
String class has a static method valueOf() which takes int as argument and converts into string.

Program #2: Java Example program to convert int to string using valueOf() method.

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
Integer i = new Integer(64);
//converting integer to string by calling valueOf() method on String clas
String str= String.valueOf(i);
System.out.println(str);
int number=123;
String numberstr= String.valueOf(number);
System.out.println(numberstr);
}
}

Output:

3.Convert Integer / int to String using new Integer(int).toString()

And here by creating Integer object and directly calling tostring method.
We can convert into to string directly with one statement this will be done by using Integer(int).toString()

Program #3: Java Example program to convert int to string using new Integer(int ).toString()

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
int number=23;
String numberstr= new Integer(number).toString();
System.out.println(numberstr);
}
}

Output:

4.Convert Integer / int to String using String.format() method

Another alternative way to convert int t string is by calling String.format method.
String.format ("%d", number);

Program #4: Java Example program to convert int to string using String.format() method

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
int number=23;
String numberstr= String.format ("%d", number);
System.out.println(numberstr);
}
}

Output:

5.Convert Integer / int to String using DecimalFormat

Another alternative way to convert int t string is by java.text.DecimalFormat
DecimalFormat class mainly used to represent numbers in formats.
Decimal format class providing format() method to convert int to string with specified format.

Program #5: Java Example program to convert int to string using DecimalFormat class

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
int number=23;
DecimalFormat obj= new DecimalFormat("#");
String numberstr= obj.format(number);
System.out.println(numberstr);
DecimalFormat objct= new DecimalFormat("#,###");
String numberstr1= objct.format(3400);
System.out.println(numberstr1);
}
}

Output:

23
3,400

6.Convert Integer / int to String using StringBuffer / StringBuilder

StringBuffer and StringBuilder classes also providing toString() method to convert int to string

Program #6: Java Example program to convert int to string using StringBuffer and StringBuilder

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
int number=234;
StringBuffer sf=new StringBuffer();
sf.append(number);
String numberstr= sf.toString();
System.out.println(numberstr);
StringBuilder sb=new StringBuilder();
sb.append(number);
String nstr= sb.toString();
System.out.println(nstr);
}
}

Output:

7.Convert Integer / int to String directly by adding to ""

We can convert a number to string simply by concatenating to "".
But it is not recommended to use.

Program #7: Java Example program to convert int to string by concat to ""

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
int number=8538;
String numberstr= ""+number;
System.out.println(numberstr);
}
}

Output:

8538

8.Convert Integer / int to String using Special radix.

Program #8: Java Example program to convert int to string using special radix

package convertintegertostring.java;
public class IntegerToString {
/**
* @ website: www.InstanceOfJava.com
*/
public static void main(String[] args) {
int number=536;
String binaryString = Integer.toBinaryString(number);
System.out.println(binaryString);
String octalString = Integer.toOctalString(number);
System.out.println(octalString);
String hexString = Integer.toHexString(number);
System.out.println(hexString);
String customString = Integer.toString(number, 7);
System.out.println(customString);
}
}

Output:

1000011000
1030
218
1364

8 different ways to convert int to string in java

Output:

64
64
536
536
3,400
536
536
1000011000

Deep copy in java example program

Posted by: Instanceofjava Posted date: 6:20 PM / comment : 0 java Collections interview Questions , java programming interview questions

Creating a copy of the object can be done in two ways
Shallow copy and deep copy. we have already discussed about shallow copy
Shallow copy in java example program
In shallow copy of object only object reference will be copied and if we change any data inside object changes will reflect in cloned object also this means both are referring to same object.

Deep copy / Deep cloning in Java

In deep copy completely a new object will be created with same data.
If we change the data inside original object wont reflect in deeply cloned object.

Program #1: Java example program to demonstrate deep copy / deep cloning

Sample :

package com.shallowcopyvsdeppcopy;
public class Sample {
int a;
int b;
Sample (int a, int b){
this.a=a;
this.b=b;
}
}

Empclone :

package com.shallowcopyvsdeppcopy;
public class empclone implements Cloneable {
Sample s;
int a;
empclone(int a, Sample s){
this.a=a;
this.s=s;
}
public Object clone()throws CloneNotSupportedException{
return new empclone(this.a, new Sample(this.s.a,this.s.a));
}
public static void main(String[] args) {
empclone a= new empclone(2, new Sample(3,3));
empclone b=null;
try {
b=(empclone)a.clone();
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(a.s.a);
System.out.println(b.s.a);
a.s.a=12;
System.out.println(a.s.a);
System.out.println(b.s.a);
}
}

OutPut:

What is the difference between shallow copy and deep copy:

When we create a shallow copy of the object only reference will be copied
When we create deep copy of the object totally new object with same data will be created.
Shallow copy and deep copy will be done by using Cloneable interface in java.

Shallow copy in java example program

Posted by: Instanceofjava Posted date: 2:15 PM / comment : 0 Core java Interview Questions , java programming interview questions

We create exact copy of the object using Cloneable in java.
We need to override object class clone() method.
This is also called clone of the object.
So we can create copy of object using two different way
1. Shallow copy
2. Depp copy

Shallow copy / Shallow cloning in java

In Shallow copy object reference will be copied instead of copying whole data of the object.
So the newly created object will be another reference for existing with same data means shallow copy of the object.
Whenever we change data in the original object same changes made to new object also because both are pointing to same object.

Program #1: Java example program to demonstrate shallow copy / shallow cloning

Example:

package com.shallowcopyvsdeppcopy;
public class Example{
int a;
int b;
Example(int a, int b){
this.a=a;
this.b=b;
}
}

Empclone :

package com.shallowcopyvsdeppcopy;
public class Empclone implements Cloneable {
Example e;
int a;
Empclone (int a, Example es){
this.a=a;
this.e=e;
}
public Object clone()throws CloneNotSupportedException{
return super.clone();
}
public static void main(String[] args) {
Empclone a= new Empclone (2, new Example(3,3));
Empclone b=null;
try {
b=(Empclone )a.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
System.out.println(a.e.a);
System.out.println(b.e.a);
a.e.a=12;
System.out.println(a.e.a);
System.out.println(b.e.a);
}
}

Output:

Print Pascals triangle using java program

Posted by: Instanceofjava Posted date: 9:35 PM / comment : 0 java interview programs , java programming interview questions

Pascals triangle means arranging numbers in pascal triangle format.
First row starts with number 1.
Here is the pascal triangle with 8 rows.

The sum of all numbers in each row will be double the sum of all numbers in above row
The diagonals adjacent to the border diagonals of 1's contains natural numbers in order

Program #1: Java example program to print numbers in pascals triangle pattern.

package interviewprograms.instanceofjava;
import java.util.Scanner;
/*
* www.instanceofjava.com
*/
public class PasclasTriangleProgram {
public static void main(String args[]){
Scanner in = new Scanner(System.in);
System.out.println("Enter number of rows ");
int rows= in.nextInt();
for(int i =0;i<rows;i++) {
int number = 1;
System.out.format("%"+(rows-i)*2+"s","");
for(int j=0;j<=i;j++) {
System.out.format("%4d",number);
number = number * (i - j) / (j + 1);
}
System.out.println();
}
}
}

Output:

Enter number of rows
8
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
1 7 21 35 35 21 7 1

1.Pattern Programs in java Part-1

2.Pattern Programs in java Part-2

3.Pattern Programs in java Part-3

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