java over view

What is Java?

Java is simple language
   easy to understand & based on c++
   Java removed many confusing & easrly used features.
            like:explicit pointers, operater overloading
   by default java provides Garbage collection automatically & memory management

Java is platform independent
Object oriented
Java is robust langulage: beacause it is used in consumer applicatoins, mission critical applications & navigation systems.


What is java Main method

public static void main (String[] args)

public-> so JVM can execute the method from anywhere
static-> method is to be called without object
void-> main method doesnt returns anything.
main()-> configured in JVM
String[]-> main method accepts a single arguments of an array of elements of type string.

System.out.println()

System->pre defined class
out->variable type output stream connected to console
println()-> method


is Main method is compulsory in Java?

<5 main method is not compulsory in java because static block was executed & doesnt need object to call method.

>=6 main method is compulsory .
     compilation is successful but we will get run time error as
"Erro main method not found in class test. Please define the main method as public static vooid main(String[] args)"

normal Interview Questions and answers

>write a program to check wheather given string is a plindrome or not?
ex: maaM -->true

code:

public class program{

public static void main(String... args)
{

System.out.println(isPalindrome(""Maam)) ;
}
 public boolean isPalindrome(String word)
  {
    word = word.toLowerCase();
    boolean result = false;
    String myword = "";
    for(int i = word.lenght()-1;i>=0;i--)
         {

             myword = myword + word.charAt(i);
          }

 if(word.equals(myword)
{ result = true;}
return result;
 }
}






Question:

User interface contains two types of user input controls: TextInput, which accepts all characters and NumericInput, which accepts only digits.
Implement the class TextInput that contains:

• Public method void add(char c) - adds the given character to the current value
• Public method String getValue() - returns the current value

Implement the class NumericInput that:

• Inherits TextInput
• Overrides the add method so that each non-numeric character is ignored

For example, the following code should output "10":

TextInput input = new NumericInput();
input.add('1');
input.add('a');
input.add('0');
System.out.println(input.getValue());

Answer:

class TextInput {
     String input = "";
     String output = "";
    public void add(char ch)
    {
        this.input = this.input+ch;
    }
    public String getValue(){
       
        return this.input;
   
    }
   
}

class NumericInput extends TextInput {
    public void add(char ch)
    {
       
        if(Character.isDigit(ch))
        {
            super.input = super.input + ch;
        }
    }
   
}

public class UserInput {
    public static void main(String[] args) {
        TextInput input = new NumericInput();
        input.add('1');
        input.add('a');
        input.add('0');
        input.add('0');
        input.add('h');
        System.out.println(input.getValue());
    }
}

Write a function that, given a list and a target sum, returns zero-based indices of any two distinct elements whose sum is equal to the target sum. If there are no such elements, the function should return null.
For example, findTwoSum(new int[] { 1, 3, 5, 7, 9 }, 12) should return any of the following tuples of indices:

• 1, 4 (3 + 9 = 12)
• 2, 3 (5 + 7 = 12)
• 3, 2 (7 + 5 = 12)
• 4, 1 (9 + 3 = 12)

answer

public class TwoSum {
    public static int[] findTwoSum(int[] list, int sum) {
        for(int i=0;i<list.length-1;i++)
        {
            for(int j=i+1;j<list.length;j++)
            {
                //System.out.println(i + " " +j);
                if(list[i]+list[j] == sum)
                {
                    return new int[] {i,j};
                }
            }
            //System.out.println(list[i]);
        }
        return new int[]{0,0};
    }

    public static void main(String[] args) {
        int[] indices = findTwoSum(new int[] { 1, 3, 5, 7, 9 }, 12);
        System.out.println(indices[0] + " " + indices[1]);
    }
}