Convert String to int in Java

How to convert string to int in Java

During work suddenly we need to make check on int value but in first we take values in string which is not required by logically.. for this we need to convert string in int then we can compare this int into string to compare right value.
we are using parseInt() with argument to convert string into string

 Using Integer.parseInt

String strg="5678";
int num = Integer.parseInt(strg);

The value of num would be 5678.

Note: 
All characters in the String must be digits
however the first character can be a minus ‘-‘ sign. 

String str="-5678";
int num = Integer.parseInt(str);

The value of num would be -5678

Integer.parseInt
throws
NumberFormatException If the String is not valid for conversion for example

String str="15ab";
 int num = Integer.valueOf(str);

This set of statement would throw NumberFormatException.
you would see a compilation error like this:

Exception in thread "main" java.lang.NumberFormatException: For input string: "15ab"
 at java.lang.NumberFormatException.forInputString(Unknown Source)
 at java.lang.Integer.parseInt(Unknown Source)
 at java.lang.Integer.parseInt(Unknown Source)

Example:

public class Example{
   public static void main(String args[]){
       String str="567";
       int num1 = 100;
       int num2 = Integer.parseInt(str);
       int sum=num1+num2;
       System.out.println("Sum is: "+sum);
   }
}

Output:

Sum is: 667

Using Integer.valueOf

Integer.valueOf works same as Integer.parseInt. It also converts a String into an integer value. This is how it can be used:

String strg="11";
int num = Integer.valueOf(strg);

The value of num would be 11.

It also allows first character of String to be a minus ‘-‘ sign.

String strg="-22";
 int num = Integer.valueOf(strg);

Value of num would be -22.

Like parseInt method it also throws NumberFormatException when the all the characters in the String are not digits. For example a String with value “55aa22″ would cause such exception during conversion.

Example2:

public class Example2{
   public static void main(String args[]){
       String strg="333";
       int num1 = 100;
       //num2 would be having a negative value
       int num2 = Integer.valueOf(strg);
       int sum=num1+num2;
       System.out.println("Sum is: "+sum);
   }
}

Output:

Sum is: 433