Top 70 Java Program Interview Questions

package com.softwaretestingo.sto000collectedpgms.interviewprograms;
import java.util.Arrays;
public class STO0008_1_ReverseStringByPreservingSpaces 
{
	/*
	 * Input : he is a good boy 
	 * Output: yo bd o ogas ieh
	 */
	public static void main(String[] args) 
	{
		String input="he is a good boy";
		System.out.println("Input: "+input);
		String[] split=input.split(" ");
		
		StringBuilder sb=new StringBuilder(input.replaceAll(" ", ""));
		sb.reverse();
		
		int count=0;
		for(String o:Arrays.asList(split).subList(0, split.length-1))
		{
			count=count+o.length();
			sb.insert(count, " ");
			count++;
		}
		System.out.println("Output: "+sb);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms.strings;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
public class STO0013_0_ExpandCharByCount 
{
	/**
	 * Input 1B3A2D4C 
	 * Output BAAADDCCCC
	 * WALLMART
	 */
	public static void main(String[] args)
	{
		String s = "1B3A2D4C";
		System.out.println("Input: "+s);
		String[] sArray = s.split("");
		List<String> intList = new ArrayList<>();
		List<String> sList = new ArrayList<>();
		for(String temp : sArray) {
			if(temp.matches("[a-zA-Z]")) {
				sList.add(temp);
			}
			else 
			{
				intList.add(temp);
			}
		}
		Map<String, Integer> map = new LinkedHashMap<>();
		Iterator<String> itr1 = sList.iterator();
		Iterator<String> itr2 = intList.iterator();
		while(itr1.hasNext() && itr2.hasNext()) 
		{
			map.put(itr1.next(), Integer.parseInt(itr2.next()));
		}
		System.out.print("Output: ");
		for(Map.Entry<String, Integer> m : map.entrySet()) 
		{
			for(int i=0;i<m.getValue();i++)
			{
				System.out.print(m.getKey());
			}
		}
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms.strings;
public class STO0020_1_PrintEachCharacterConsecutiveMentionedTimes 
{
	// Interview Questions Asked In Unify technologies
	// Suppose input string is "c3d4a2" then output should be "cccddddaa"
	public static void main(String[] args) 
	{
		String s="c3d4a2";
		String ans="";

		for (int i = 0; i<=s.length()-1; i++) 
		{
			String r=String.valueOf(s.charAt(i));
			int rep= Integer.valueOf(String.valueOf(s.charAt(i+1)));		

			for (int j =1 ; j<=rep; j++) 
			{
				ans=ans+r;
			}
			i=i+1;
		}
		System.out.println("Input: "+s);
		System.out.print("Output: "+ans);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms.reverse;
public class STO0029_0_ReverseSentence 
{
	/*
	 * Input - Hi I am Naveen I need and answer 
	 * Output - answer and deen I Naveen ma I Hi
	 */
	public static void main(String[] args) 
	{
		String str = "Hi I am Naveen I need and answer";
		System.out.println("Input: "+str);
		String[] sp=getPattern(str);
		System.out.print("Output: ");
		// print Array
		for(int j=sp.length-1; j>=0; j--) 
		{
			System.out.print(sp[j] + " ");
		}
	}
	private static String[] getPattern(String revStr)
	{
		String[] splitStr = revStr.split(" ");
		for ( int j = splitStr.length-3; j>=0 ; j=j-3)
		{
			String temp=splitStr[j];
			StringBuilder sb = new StringBuilder(temp);
			splitStr[j] = sb.reverse().toString();
		}
		return splitStr ;
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms.reverse;
public class STO0029_1_ReverseSentence 
{
	/*
	 * Input - Hi I am Naveen I need and answer 
	 * Output - answer and deen I Naveen ma I Hi
	 */
	public static void main(String[] args) 
	{
		String input = "Hi I am Naveen i need and answer";
		System.out.println("Input: "+input);
		String[] inputArr=input.split(" ");
		String outputStr = "" ;
		int j = 0 ;
		for (int i=inputArr.length-1; i>=0 ; i-- ) 
		{
			++ j ;
			String indexedStr = "";
			if (j%3==0)
			{
				for (int k=inputArr[i].length()-1 ; k>=0 ; k--) 
				{
					indexedStr = indexedStr + inputArr[i].charAt(k);
				}
			}
			else 
			{
				indexedStr=inputArr[i];
			}
			outputStr = outputStr + " " + indexedStr;
		}
		System.out.println("Output: "+outputStr.trim());
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms.strings;
public class STO0027_0_SumOfNumbersInString 
{
	/**
	 * Write a program that calculate the sum of all numbers present in alphanumeric
	 * string in sentence.
	 * 
	 * Input: "1a b23c de45f" 
	 * Output: 69 (1 + 23 + 45)
	 */
	public static void main(String[] args) 
	{
		String str = "1a b23cd e45f";
		System.out.println("Input: "+str);
		int sum = 0;

		String number = "";
		for (int i = 0; i <=str.length()-1; i++) 
		{
			if (Character.isDigit(str.charAt(i))) 
			{
				number += str.charAt(i);
			} 
			else if (!number.isEmpty()) 
			{
				sum += Integer.parseInt(number);
				number = "";
			}
		}
		System.out.println("Sum Of All Numbers: "+sum);
	}
}

package com.softwaretestingo.sto000collectedpgms.interviewprograms.strings;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class STO0027_1_SumOfNumbersInString 
{
	/**
	 * Write a program that calculate the sum of all numbers present in alphanumeric
	 * string in sentence.
	 * 
	 * Input: "1a b23c de45f" 
	 * Output: 69 (1 + 23 + 45)
	 */
	public static void main(String[] args) 
	{
		String str = "1a b23cd e45f";
		System.out.println("Input: "+str);
		int sum = 0;
		String pattern = "\\d+";
		Pattern p = Pattern.compile(pattern);
		Matcher m = p.matcher(str);
		while (m.find()) 
		{
			sum = sum + Integer.parseInt(m.group());
		}
		System.out.println("Output: "+sum);
	}
}