How to Convert String to Integer in Java
How to convert String to int in Java
You need to convert String into int if you want to perform a mathematical operation on string which contains digits. To do so, you need to perform the conversion from String to int.
You can convert String to int in two ways:
- Using Integer.parseInt() method
- Using Integer.valueOf() method
Using Integer.parseInt() method
The paresInt() is the static method of Integer wrapper class under java.lang package.
Example-
In the following example, number is a variable of type String that contains digits “10” as string. num1 is a variable of type integer that contains value 20. num2 is the variable of type integer which stores the converted value of str. Integer is a class. paresInt() is the static method that takes str as an argument and returns a primitive int value. sum is a variable of type integer which stores the value after addition. The println statement prints the value of sum.
public class StringTointExample
{
public static void main(String args[])
{
String str="10";
int num1 = 20;
int num2 = Integer.parseInt(str);
int sum = num1+num2; //num2 adds the converted value of str into num1
System.out.println("Befor conversion: "+str);
System.out.println("After conversion Sum is: "+sum);
}
}
Output-
Before conversion: 10 After conversion Sum is: 30
Remember: All characters must be in digits; the number can have a minus sign.
Valid Conversion
- String number=”-369”;
Invalid Conversion
- String number=”369a”;
- String number=”abcd”;
If you define a String as above, Integer.parseInt() throws “NumberFormatException”, because it is not a valid conversion.
Exception
Exception in thread "main" java.lang.NumberFormatException: For input string: "369a" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Integer.parseInt(Integer.java:580) at java.lang.Integer.parseInt(Integer.java:615) at StringToIntExample.main(StringToIntExample.java:6)
Using Integer.valueOf() method
Integer.valueOf() works same as Integer.parseInt(String). It also converts a String to int value. It also throws NumberFormatException.
Example-
In the following example, str is a variable of type String that contains digits “-10” as string. num1 is a variable of type integer that contains value 110. num2 is a variable of type integer that stores the converted value of str. Integer is a wrapper class. valueOf() is the method that returns an integer instance representing the specified int value. val is a variable that stores the sum of num1 and num2. First println statement prints the String str and second println prints the value of val after performing addition.
public class StringTointExample1
{
public static void main(String args[])
{
String str="-10";
int num1 = 110;
int num2 = Integer.valueOf(str);
int val = num1+num2; //num2 adds the converted value of str into num1
System.out.println("Before conversion: "+str);
System.out.println("After addition value is: "+val);
}
}
Output-
Before conversion: -10 After addition value is: 100
Difference Between Integer.valueOf() and Integer.parseInt()
There is a difference between Integer.valueOf() and Integer.parseInt(). The Integer.valueOf() method returns an object of Integer class whereas the Integer.parseInt() method returns a primitive int value.
If you need the primitive int datatype, then use parseInt() method. If you want wrapper Integer object, then use the valueOf() method.