Top 70 Java Program Interview Questions

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
public class STO0003_0_NoOfOccuranceOfSubstringInString 
{
	/*
	 * String s =“lekhale” How many times “le” is Getting repeated, write a code to
	 * find out using java.
	 */
	public static void main(String[] args) 
	{

		String s="lekhale";
		System.out.println("Input:  "+s);
		//This will print the length of the string (7)
		//System.out.println(s.length());

		//this will give you the total length of the string after replace le with space(3)
		//System.out.println((s.replaceAll("le","").length()));

		//Need to divide the number of character 
		int result = (s.length()-s.replaceAll("le","").length())/2;
		System.out.println("Output: "+result);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
public class STO0003_1_NoOfOccuranceOfSubstringInString 
{
	/*
	 * String s =“lekhale” How many times “le” is Getting repeated, write a code to
	 * find out using java.
	 */
	public static void main(String[] args) 
	{

		String s = "lekhale";
		System.out.println("Input: "+s);
		int count = 0;
		int index = s.indexOf("le");
		while (index != -1) 
		{
			count++;
			index = s.indexOf("le", index + 1);
		}
		System.out.println("Output: "+"The substring 'le' is repeated " + count + " times in the given string.");
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
public class STO0003_2_NoOfOccuranceOfSubstringInString 
{
	public static void main(String[] args) 
	{
		String str="abababababaabb";
		String sub = "bab";

		int n = str.length();
		int m = sub.length();

		// index=-1 in case of no match, otherwise >=0(first match position)
		int index=str.indexOf(sub), i=index+1, count=(index>=0)?1:0;
		//System.out.println(i+" "+index+" "+count);

		// i will traverse up to only (m-n) position
		while(index!=-1 && i<=(n-m))
		{   
			index=str.substring(i, n).indexOf(sub);
			count=(index>=0)?count+1:count;
			i=i+index+1;  
			//System.out.println(i+" "+index);
		}
		System.out.println("Original String: "+str);
		System.out.println("Sub String: "+sub);
		System.out.println("Total Number Of Substring Appears: "+count);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class STO0003_3_NoOfOccuranceOfSubstringInString 
{
	static int countMatches(Pattern pattern, String string)
	{
		Matcher matcher = pattern.matcher(string);

		int count = 0;
		int pos = 0;
		while (matcher.find(pos))
		{
			count++;
			pos = matcher.start() + 1;
		}

		return count;
	}
	public static void main(String[] args) 
	{
		Scanner sc=new Scanner(System.in);
		System.out.print("Enter a sentence please:");
		String str = sc.nextLine();
		System.out.print("Enter a SubString:");
		String sub=sc.next();
		Pattern pattern = Pattern.compile(sub);
		int count = countMatches(pattern, str);
		System.out.println("No Of Times Sub String Appears: "+count);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
import java.util.Scanner;
public class STO0003_4_NoOfOccuranceOfSubstringInString 
{
	public  static  int getCountSubString(String str , String sub)
	{
		int n = 0, m = 0, counter = 0, counterSub = 0;
		while(n < str.length())
		{
			counter = 0;
			m = 0;
			while(m < sub.length() && str.charAt(n) == sub.charAt(m))
			{
				counter++;
				m++; n++;
			}
			if (counter == sub.length())
			{
				counterSub++;
				continue;
			}
			else if(counter > 0)
			{
				continue;
			}
			n++;
		}

		return  counterSub;
	}
	public static void main(String[] args) 
	{
		int count;
		Scanner scanner = new Scanner(System.in);
		System.out.print("Enter a sentence please:");
		String str = scanner.nextLine();
		System.out.print("Enter a Substring");
		String sub=scanner.next();
		STO0003_4_NoOfOccuranceOfSubstringInString obj=new STO0003_4_NoOfOccuranceOfSubstringInString();
		count=obj.getCountSubString(str, sub);

		System.out.println("Original String: "+str);
		System.out.println("Sub String: "+sub);
		System.out.println("Total Number Of Substring Appears: "+count);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
import java.util.Scanner;
public class STO0003_5_NoOfOccuranceOfSubstringInString 
{
	public static void main(String[] args) 
	{
		Scanner scanner = new Scanner(System.in);
		System.out.print("Enter a sentence please:");
		String str = scanner.nextLine();
		System.out.print("Enter a sentence please:");
		String sub=scanner.next();

		int count =0;
		int findStrLength = sub.length();
		for(int i=0;i<str.length();i++)
		{
			if(sub.startsWith(Character.toString(str.charAt(i))))
			{
				if(str.substring(i).length() >= findStrLength)
				{
					if(str.substring(i, i+findStrLength).equals(sub))
					{
						count++;
					}
				}
			}
		}


		System.out.println("Original String: "+str);
		System.out.println("Sub String: "+sub);
		System.out.println("Total Number Of Substring Appears: "+count);
	}
}