Sometimes there is a need to convert a String to an Integer value. Even if a String is made up of digits like 1,2,3 etc, any arithmetic operation cannot be performed on it until it gets converted into an integer value. In this tutorial we will see two ways to convert String to int.
Method 1: Convert String to int using Integer.parseInt(String)
String str3="1234"; int num3 = Integer.parseInt(str3);
The value of num3 would be 1234.
Note: All characters in the String must be digits however the first character can be a minus ‘-‘ sign. For example:
String str="-1234"; int num = Integer.parseInt(str);
The value of num would be -1234
Integer.parseInt() throws NumberFormatException, if the String is not valid for conversion. For example:
String str="1122ab"; int num = Integer.valueOf(str);
This would throw NumberFormatException. you would see a compilation error like this:
Exception in thread "main" java.lang.NumberFormatException: For input string: "1122ab" at java.lang.NumberFormatException.forInputString(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at java.lang.Integer.parseInt(Unknown Source)
Lets see the complete code for String to int conversion.
Java Convert String to int Example using Integer.parseInt(String)
public class Example{
public static void main(String args[]){
String str="123";
int num1 = 100;
//converting the string to an int value
int num2 = Integer.parseInt(str);
int sum=num1+num2;
System.out.println("Result is: "+sum);
}
}
Output:
Result is: 223
Method 2: Convert String to int using Integer.valueOf(String)
Integer.valueOf(String) works same as Integer.parseInt(String). It also converts a String to int value. However there is a difference between Integer.valueOf(String) and Integer.parseInt(String), the valueOf(String) method returns an object of Integer class whereas the parseInt(String) method returns a primitive int value. The output of the conversion would be same whichever method you choose. This is how it can be used:
String str="1122"; int num = Integer.valueOf(str);
The value of num would be 1122.
It also allows first character of String to be a minus ‘-‘ sign.
String str="-1122"; int num = Integer.valueOf(str);
Value of num would be -1122.
Similar to the parseInt(String) method it also throws NumberFormatException when all the characters in the String are not digits. For example a String with value “11aa22” would throw an exception.
Lets see the complete code for conversion using this method.
Java Convert String to int Example using Integer.valueOf(String)
public class Example2{
public static void main(String args[]){
String str="-234";
int num1 = 110;
//num2 would be having a negative value
int num2 = Integer.valueOf(str);
int sum=num1+num2;
System.out.println("Result is: "+sum);
}
}
Output:
Result is: -124
Lets see another interesting example of String to int conversion.
Convert a String to int with leading zeroes
In this example, we have a string made up of digits with leading zeroes, we want to perform an arithmetic operation on that string retaining the leading zeroes. To do this we are converting the string to int and performing the arithmetic operation, later we are converting the output value to string using format() method.
public class Example{
public static void main(String args[]){
String str="00000678";
/* String to int conversion with leading zeroes
* the %08 format specifier is used to have 8 digits in
* the number, this ensures the leading zeroes
*/
str = String.format("%08d", Integer.parseInt(str)+102);
System.out.println("Output String: "+str);
}
}
Output:
Output String: 00000780
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- Java convert int to String example
- Java convert String to long example
- Java convert String to double example
- Java convert StringBuffer to String example
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