InstanceOfJava

Java Program to Count the number of occurrences of a char in a String?

Posted by: Instanceofjava Posted date: 11:15 AM / comment : 2 Core java Interview Questions

Solution #1:

package com.javatutorial;
import java.util.Scanner;
public class CountNumberofChars {
public static void main(String[] args) {
String str = "";
Scanner in= new Scanner(System.in);
System.out.println("Please enter a String");
str=in.nextLine();
System.out.println("Please enter a Character");
String chr=in.next();
int charCount = str.length() - str.replaceAll("a", "").length();
System.out.println("Number of occurances of given character:"+charCount);
}
}

Output:

Please enter a String
Java
Please enter a Character
a
Number of occurances of given character:2

Solution #2:

package com.javatutorial;
import java.util.Scanner;
public class CountNumberofChars {
public static int countOccurrences(String find, String string)
{
int count = 0;
int indexOf = 0;
while (indexOf > -1)
{
indexOf = string.indexOf(find, indexOf + 1);
if (indexOf > -1)
count++;
}
return count;
}
public static void main(String[] args) {
int charCount=countOccurrences("a", "Instance of Java");
System.out.println("Number of occurrences of given character:"+charCount);
}
}

Output:

Number of occurrences of given character: 3

Java experience interview programming questions on Strings

Java program To Count the number of words in a String

Posted by: Instanceofjava Posted date: 10:53 AM / comment : 1 Core java Interview Questions

package com.javatutorial;
public class CountNumberofWords {
public static void main(String[] args) {
String s="";
int count=0;
Scanner in = new Scanner(System.in);
System.out.println("Please enter a String");
s=in.nextLine();
char ch[]= new char[s.length()];
for(int i=0;i<s.length();i++)
{
ch[i]= s.charAt(i);
if( ((i>0)&&(ch[i]!=' ')&&(ch[i-1]==' ')) || ((ch[0]!=' ')&&(i==0)) )
count++;
}
System.out.println("Number of words in given String: "+count);
}
}

Output:

Please enter a String
Java Tutorial
Number of words in given String: 2

Pattern Program in java Part-3

Posted by: Instanceofjava Posted date: 10:25 AM / comment : 0 concept and program

Program #1: java program to print pyramid of stars using for loop in below format

*
**
***
****
*****
******
*******
********
*********
**********

package com.learnJavaOnline;
public class PrintStarsFormat {
public static void main(String[] args) {
int numberOfStars=10;
for (int row = 1; row <= 10; row++) {
for(numberOfStars = 1; numberOfStars <= row; numberOfStars++) {
System.out.print("*");
}
System.out.println();
}
}
}

Output:

*
**
***
****
*****
******
*******
********
*********
**********

Program #2: java program to print pyramid of stars using for loop in below format

**********
*********
********
*******
******
*****
****
***
**
*

package com.learnJavaOnline;
public class PrintStarsPyramid {
public static void main(String[] args) {
int numberOfStars=10;
for(int i=numberOfStars; i>0 ;i--){
for(int j=0; j < i; j++){
System.out.print("*");
}
System.out.println("");
}
}
}

Output:

**********
*********
********
*******
******
*****
****
***
**
*

Program #3 java program to print pyramid of stars using for loop in below format

*
**
***
****
*****
******
*******
********
*********
**********
**********
*********
********
*******
******
*****
****
***
**
*

package com.learnJavaOnline;
public class PrintStarsPyramid {
public static void main(String[] args) {
int numberOfStars=10;
for(int i=1; i<= numberOfStars ;i++){
for(int j=0; j < i; j++){
System.out.print("*");
}
System.out.println("");
}
for(int i=numberOfStars; i>0 ;i--){
for(int j=0; j < i; j++){
System.out.print("*");
}
System.out.println("")}
}
}

Output:

*
**
***
****
*****
******
*******
********
*********
**********
**********
*********
********
*******
******
*****
****
***
**
*

Print Pascals triangle using java program

Pattern Program in java Part-2

Posted by: Instanceofjava Posted date: 11:41 PM / comment : 0 concept and program

#4 Java Program to print Numbers in Below pattern

1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7
   1 2 3 4 5 6
    1 2 3 4 5
     1 2 3 4
      1 2 3
       1 2
        1

package com.learnJavaOnline;
public class NumbersFormat {
public static void main(String[] args) {
int r, c1,c2;
for (r = 1; r <= 10; r++) {
for (c1 = 1; c1 <r; c1++) {
System.out.print(" ");
}
for (c2 = 1; c2 <= 10 - r; c2++) {
System.out.print(c2 + " ");
}
System.out.println("");
}
}
}

Output:

1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7
1 2 3 4 5 6
1 2 3 4 5
1 2 3 4
1 2 3
1 2
1

#5 Java Program to Print Numbers in Below pattern:

        1
       1 2
      1 2 3
     1 2 3 4
    1 2 3 4 5
   1 2 3 4 5 6
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10

package com.learnJavaOnline;
public class NumbersFormat {
public static void main(String[] args) {
int r, c1,c2;
for (r = 1; r <= 10; r++) {
for (c1 = 1; c1 <10-r; c1++) {
System.out.print(" ");
}
for (c2 = 1; c2 <= r; c2++) {
System.out.print(c2 + " ");
}
System.out.println("");
}
}
}

Output:

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10

Print Pascals triangle using java program

Pattern Program in java Part-1

Posted by: Instanceofjava Posted date: 11:12 PM / comment : 0 concept and program

#1 Java Program To print Numbers in Below pattern:

              1
             2 3
            4 5 6
           7 8 9 10
         11 12 13 14 15

package com.javatutorial;
public class NumbersFormat {
public static void main(String[] args) {
int num=15;
int temp=1;
for (int i = 1; i <= num; i++)
{
for (int k = i; k <num; k++)
System.out.print(" ");
for (int j =1; j <= i; j++){
System.out.print("" +temp+ " ");
temp++;
if(temp>15){
break;
}
}
System.out.println();
if(temp>15){
break;
}
}
}
}

Output:

              1
             2 3
            4 5 6
           7 8 9 10
          11 12 13 14 15

# Java Program to print Numbers in Below Format:

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10

package com.learnJavaOnline;
public class NumbersFormat {
public static void main(String[] args) {
int r, c;
for (r = 1; r <= 10; r++) {
for (c = 1; c <= r; c++) {
System.out.print(c + " ");
}
System.out.println("");
}
}
}

Output:

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10

#3 Java Program to print numbers in below format

1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7
1 2 3 4 5 6
1 2 3 4 5
1 2 3 4
1 2 3
1 2
1

package com.learnJavaOnline;
public class NumbersFormat {
public static void main(String[] args) {
int r, c;
for (r = 1; r <= 10; r++) {
for (c = 1; c <= 10-r; c++) {
System.out.print(c + " ");
}
System.out.println("");
}
}
}

Output:

1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7
1 2 3 4 5 6
1 2 3 4 5
1 2 3 4
1 2 3
1 2
1

Print Pascals triangle using java program

Collection Framework Tutorial

Posted by: Instanceofjava Posted date: 3:30 PM / comment : 0 Collections

Limitations of Arrays:

Arrays are fixed in size. need to estimate the size of an array while declaration itself. once array created we can not increase the size of an array.
Arrays can hold only homogeneous data elements. Means we can add same type of elements in an array. While declaring an array we need to mention the data type.
int a[]= new int[10];

By using Object array we can add heterogeneous elements to the array.
Object o= new Object[10];
There is no underlying data structure for arrays.
Arrays are not recommended to use with respect to memory.
Performance wise arrays are good to use.

Collections

Java Collection framework added in J2SE 1.2 release.
Collections are set of classes and interfaces.
By using Collections we can store and manipulate objects easily.
Collections can hold heterogeneous data elements.
Collections are no fixed in size and dynamically increase in size.
Collection of objects. No primitives.
All collection classes having underlying data structure.
Collections are good with respect to memory. Bad with respect to performance.

Collection interface Hierarchy:

java.util package contains all collections classes and interfaces.
Lets see collection interface hierarchy.
under Collection. Set , List , Queue are the sub interfaces.

Collections Abstract classes and classes:

Let us see all the abstract classes implementing all the above interfaces and classes which extending these abstract classes.
To Collect Objects in array format we choose Collection hierarchy classes.
Main abstract class is AbstractCollection.
AbstractSet
AbstractList
AbstractQueue
AbstractSequentialList
All the classes in Collection hierarchy are
TreeSet
HashSet
LinkedHashSet
LinkedList
ArrayList
Vector
Stack
PriorityQueue
To collect unique elements we must choose Set implemented classes
To collect unique and duplicate elements in indexed order we choose List implemented classes.
To retrieve elements in FIFO manner we choose Queue implemented classes.

Map Hierarchy:

In this hierarchy Hashtable and properties classes are avilable since java 1.0.
LinkedHashMap class is available since java 1.4
NavigableMap is available since java 6 and all other classes available since java 1.2.
SortedMap and NavigableMap are two main interfaces.
TreeMap
HashMap
LinkedHashMap
Hashtable
Properties are the classes.
To collect objects in key, value pair format we choose Map hierarchy classes.

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