Core Java Interview Questions

Using While Loop in Java

class DivisibleBy2and3And5
{
    static void divisible(int N)
    {
        int num = 1;
        while (num < N)
        {
            if (num % 2 == 0 && num % 3 == 0 && num % 5 == 0)
                System.out.print(num + " ");
            num++;	
        }
    } 
	
    public static void main(String []args)
    {
        int N = 100;
        divisible(N);
    }
} 

Using For Loop

class DivisibleBy2And3And5
{
    static void divisible(int N)
    {
        for (int num = 1; num < N; num++)
        {
            if (num % 2 == 0 && num % 3 == 0 && num % 5 == 0)
                System.out.print(num + " ");
        }
    } 
	
    public static void main(String []args)
    {
        int N = 100;
        divisible(N);
    }
} 

Checked Exception: are the exceptions that are checked at compile time. If some code within a method throws a checked exception, then the method must either handle the exception or it must specify the exception using throws keyword.

• FileNotFoundException
• IOException
• ClassNotFoundException
• SQLException 
• DataAccessException
• InvocationTargetException
• MalformedURLException

Unchecked Exception: Unchecked are the exceptions that are not checked at compiled time. 

• NullPointerException
• ArrayIndexOutOfBound
• IllegalArgumentException
• IllegalStateException
• IllegalStateException

For Input: abc123def456 Output will be: abcdef  

Check below code:

package com.test.strings;

public class RemoveNumeric 
{
	public static void main(String args[])
	{
		 String myString = "abc123def456";		 
		 System.out.println(myString.replaceAll("[0-9]", ""));
	}
}

Output: abcdef

Check below code:

package com.test.strings;

public class StringWords 
{
	public static void main(String args[])
	{
		String s = "Welcome to Java";
		
		String a[] = s.split(" ");
		
		String rev = "";
		
		for(int i = a.length - 1; i >= 0; i--)
		{
			rev = rev + a[i] + " ";
		}
		
		System.out.println(rev);
	}
}

Output: Java to Welcome

Check below code:

package com.test.arrays;

public class ThreeElementsSum 
{
	public static void main(String args[])
	{
		int sum = ThreeElementsSum.sum3(new int[] {1,2,3});
		System.out.println(sum);
	}
	
	public static int sum3(int[] nums)
	{
		return nums[0] + nums[1] + nums[2];
	}
}

Output

6

Check below code:

package com.test.strings;

public class abba 
{
	public static void main(String args[])
	{
		System.out.println(abba.makeAbba("Hi","Bye"));
		System.out.println(abba.makeAbba("Programs","Buzz"));
	}

	public static String makeAbba(String a, String b)
	{
		return(a+b+b+a);
	}
}

Output

HiByeByeHi
ProgramsBuzzBuzzPrograms

Modify and return the given map as follows: if the key "a" has a value, set the key "b" to have that value, and set the key "a" to have the value "". Basically "b" is a bully, taking the value and replacing it with the empty string.

Check below code:

package com.test.collections;

import java.util.HashMap;
import java.util.Map;

public class MapBully 
{
	public static void main(String args[])
	{
		MapBully mb = new MapBully();
		HashMap<String, String> hm = new HashMap<String, String>();
		hm.put("a","candy");
		hm.put("b","dirt");
		System.out.println(mb.mapBully(hm));
	}

	public Map<String, String> mapBully(HashMap<String, String> map) 
	{
        if(map.containsKey("a"))
        {
        	map.put("b", map.get("a"));
        	map.put("a", "");
        }
        return map;
    }
}

Output

{a=, b=candy}

Note: Both arrays will be length 1 or more.

Check Below Code:

package com.test.arrays;

public class CommonArrayEnd 
{
	public static void main(String args[])
	{
		CommonArrayEnd ca = new CommonArrayEnd();
		System.out.println(ca.commonEnd(new int[] {1, 2, 6}, new int[] {1, 2, 6}));
		System.out.println(ca.commonEnd(new int[] {1, 2, 3}, new int[] {7, 3, 2}));
		System.out.println(ca.commonEnd(new int[] {1, 2, 3}, new int[] {1}));
	}
	
	public boolean commonEnd(int[] a, int[] b) 
	{
		return (a[0] == b[0] || a[a.length-1] == b[b.length-1]);
	}
}

Output

true
false
true

Check below code:

package com.test.strings;

public class HelloName 
{
	public static void main(String args[])
	{
		HelloName hn = new HelloName();
		System.out.println(hn.helloName("Ram"));
		System.out.println(hn.helloName("Sham"));
		System.out.println(hn.helloName("X"));
	}
	
	public String helloName(String name) 
	{
		 return "Hello " + name + "!";
	}
}

Output

Hello Ram!
Hello Sham!
Hello X!

Check below code:

package com.test.arrays;

public class FirstLastEqual 
{
	public static void main(String args[])
	{
		FirstLastEqual fl = new FirstLastEqual();
		System.out.println(fl.sameFirstLast(new int[] {1, 2, 1}));
		System.out.println(fl.sameFirstLast(new int[] {1, 2, 3, 1}));
		System.out.println(fl.sameFirstLast(new int[] {1, 2, 3}));
	}
	
	public boolean sameFirstLast(int[] nums) 
	{
		if(nums.length >= 1 && nums[0] == nums[nums.length-1])
			return true;
		else
			return false;	  
	}
}

Output

true
true
false