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Array and String Programs

In this tutorial we will see some of the programs of array and string which are commonly asked with beginners in interviews. These programs will help them to build their logics in using array and string. Let's see the first program which shows how to check if a given number exist inside an array. If it exist, the program will also print it's index in the array.

Java Program to check if a number exist inside an array

 class SearchNumber
   {
     public static void main(String [] args)
       {          
          int [] numbers = {40,60,80,65,70};
          boolean isExist = false;
          int searchNumber = 80;
          int pos = -1;
          for(int i = 0; i < numbers.length; i++)
            {
              if(numbers[i] == searchNumber)
                {
                  isExist = true;
                  pos = i;
                  break;
                }
            }
          if(isExist)
              System.out.println("number "+searchNumber+" exist in the array at index = "+pos);
          else
            System.out.println("number "+searchNumber+" does not exist inside the array");
        }
   }

Output :

number 80 exist in the array at index = 2

The next program shows how to find minimum and maximum element of an array. This is one way to find the minimum and maximum element, there can be other approaches as well.

Java Program to find minimum and maximum element of an array

 class MinMaxOfArray
   {
     public static void main(String [] args)
       {          
          int [] numbers = {40,20,80,65,70,90,35,10};
          int maxValue = numbers[0];
          int minValue = numbers[0];
          for(int i=1;i < numbers.length;i++) 
            {  
              if(numbers[i] < minValue)
	         minValue = numbers[i];               
  
              if(numbers[i] > maxValue)
	         maxValue = numbers[i];
            }	
          System.out.println("Minimum number = "+minValue+" and maximum number = "+maxValue); 
        }
   }

Output :

Minimum number = 10 and maximum number = 90

The next program shows how to sort an array of integer elements in ascending order. This is one approach to sort an array, there are other approaches as well to do the same.

Java Program to sort an array

 class SortArray
   {
     public static void main(String [] args)
       {          
          int [] numbers = {40,20,80,65,70,90,35,10};   
          int length = numbers.length;  
          int temp;  
          for(int i = 0; i < length; i++) 
            {
              for(int j = i + 1; j < length; j++) 
                {
                  if(numbers[i] > numbers[j]) 
                    {
                      temp = numbers[i];
                      numbers[i] = numbers[j];
                      numbers[j] = temp;
                    }
                }
            }
          System.out.println("Array elements in ascending Order:");
          for(int n : numbers) 
              System.out.print(n + " ");      
       }
   }

Output :

Array elements in ascending Order:
10 20 35 40 65 70 80 90

The next program shows how to reverse a given string and checks if it is a palindrome string. A string is called palindrome if the reverse of the string is same as the original string. Again this is one way to reverse the string, there can be other ways as well to do the same. You can also use reverse() method of StringBuffer/StringBuilder class to reverse a given string directly but our intention is to learn the logic.

Java Program of reverse and palindrome string

 class ReverseAndPalindromeString
   {
     public static void main(String [] args)
       {          
          String str =  "abcba"; 
          String revStr = "";
          for(int i = str.length() - 1; i >= 0; i--)
            {
              revStr = revStr + str.charAt(i);
            }        
          System.out.println("Reverse string = "+revStr);
          if(revStr.equals(str))
            System.out.println("The given string is a palindrome string");
          else
            System.out.println("The given string is not a palindrome string");
       }
   }

Output :

Reverse string = abcba
The given string is a palindrome string

Let's write one more program which counts total number of occurrence of a given character inside a given string. The program shows two different approaches to count the total occurrence.

Java Program to find total count of a given character inside a given string

 class CharacterCount
   {
      public static void main(String[] args) 
        {  
          String str = "Java is easy to learn";
          char c = 'a'; 
          int count = 0;
          // First Approach
          char[] charArray = str.toCharArray();
          for(char ch : charArray)
            {
              if(ch == c)
                count++;
            }
          System.out.println("Total occurrence of character 'a' using 1st approach = "+count);
        
          // Second Approach
          int count2 = str.length() - str.replace("a", "").length();
          System.out.println("Total occurrence of character 'a' using 2nd approach = "+count2);
       }  
   }

Output :

Total occurrence of character 'a' using 1st approach = 4
Total occurrence of character 'a' using 2nd approach = 4