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String to int in Java

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In Java, while operating upon strings, there are times when we need to convert a number represented as a string into an integer type. We usually do this because we can operate with a wide flexible set of operations over strings. The method generally used to convert String to Integer in Java is parseInt() of the String class.

In this article, we will see how to convert a String to int in Java.

Java String to Int

Program to Convert Java String to int

Let us take an example straight away to get used to the working parseInt() method :

Java




// Java program to demonstrate working parseInt()
// Where No NumberFormatException is Thrown
 
// Main class
public class GFG {
    // Main driver method
    public static void main(String args[])
    {
        // Custom wide-varied inputs to illustrate
        // usage of valueOf() method
        int decimalExample = Integer.parseInt("20");
        int signedPositiveExample = Integer.parseInt("+20");
        int signedNegativeExample = Integer.parseInt("-20");
        int radixExample = Integer.parseInt("20", 16);
        int stringExample = Integer.parseInt("geeks", 29);
 
        // Print commands on console
        System.out.println(decimalExample);
        System.out.println(signedPositiveExample);
        System.out.println(signedNegativeExample);
        System.out.println(radixExample);
        System.out.println(stringExample);
    }
}


Output

20
20
-20
32
11670324



parseInt() Method in Java

There are two variants of this method:

  1. parseInt(String s): This function parses the string argument as a signed decimal integer.
  2. parseInt(String s, int radix): This function parses the string argument as a signed integer in the radix specified by the second argument.

Syntax of parseInt

public static int parseInt(String str); 
public static int parseInt(String str, int radix);

Parameters

  • str: String that needs to be converted to an integer.
  • radix: is used while the string is being parsed.

Return Type

  • Both methods convert the string into its integer equivalent. The only difference is that of the parameter radix. The first method can be considered with radix = 10 (Decimal).

Exception Thrown

Remember certain key points associated with both variants:

  1. The string can be null or of zero-length
  2. Value represented by the string is not a value of type int
  3. Specifically for the parseInt(String s, int radix) variant of the function: 
    • The second argument radix is either smaller than Character.MIN_RADIX or larger than Character.MAX_RADIX
    • Any character of the string is not a digit of the specified radix, except that the first character may be a minus sign ‘-‘ (‘\u002D’) or plus sign ‘+’ (‘\u002B’) provided that the string is longer than length 1
  4. If your String has leading zeroes, the parseInt() method will ignore them. 

Cases of parseInt() Method

Let’s take a random code snippet further understand the illustrations better.

Case 1: parseInt(“20”, 16)

returns 32 , (2)*16^1 + (0)*16^0 = 32

Case 2: parseInt(“2147483648”, 10)

throws a NumberFormatException

Case 3: parseInt(“99”, 8)

throws a NumberFormatException
Reason: 9 is not an accepted digit of octal number system

Case 4: parseInt(“geeks”, 28)

throws a NumberFormatException

Case 5: parseInt(“geeks”, 29)

returns 11670324, Reason: Number system with base 29 can have digits 0-9 followed by characters a,b,c… upto s

Case 6: parseInt(“geeksforgeeks”, 29)

throws a NumberFormatException as the Reason: result is not an integer.

Number Format Exceptions of parseInt() Method

Exceptions caused by parseInt() Method mentioned below:

Java




// Java Program to Demonstrate Working of parseInt() Method
// Where NumberFormatException is Thrown
 
// Main class
public class GFG {
    // Main driver method
    public static void main(String args[])
    {
        // NumberFormatException
        String invalidArguments = "";
       
          // invalidArguments Error empty string
         // passed
        int emptyString
            = Integer.parseInt(invalidArguments);
       
          // The Converted Intger is out of bound
          // Too large to be called Integer
        int outOfRangeOfInteger
            = Integer.parseInt("geeksforgeeks", 29);
       
          // Domain Number System
        int domainOfNumberSystem
            = Integer.parseInt("geeks", 28);
 
        // Print commands on console
        System.out.println(emptyString);
        System.out.println(outOfRangeOfInteger);
        System.out.println(domainOfNumberSystem);
    }
}


Output

Similarly, we can convert the string to any other primitive data type:

  1. parseLong(): parses the string to Long
  2. parseDouble(): parses the string to double If we want to convert the string to an integer without using parseInt(), we can use valueOf() method. It also has two variants similar to parseInt()
  3. Difference between parseInt() and valueOf(): parseInt() parses the string and returns the primitive integer type. However, valueOf() returns an Integer Object.

Note: valueOf() uses parseInt() internally to convert to integer. 

Another Approach for Converting a String to Integer

Apart from parseInt() Method in Java there is another method for conversion of String to Integer. Below is the implementation of valueOf() method that is

valueOf() Method

The Integer.valueOf() method converts a String into an Integer object. Let us understand this by an example.

Below is the implementation of the above method:

Java




// Java Program to Demonstrate
// Working of valueOf() Method
 
// Main class
public class GFG {
    // Main driver method
    public static void main(String args[])
    {
        // Custom wide-varied inputs to illustrate
        // usage of valueOf() method
        int decimalExample = Integer.valueOf("20");
        int signedPositiveExample = Integer.valueOf("+20");
        int signedNegativeExample = Integer.valueOf("-20");
        int radixExample = Integer.valueOf("20", 16);
        int stringExample = Integer.valueOf("geeks", 29);
 
        // Print statements
        System.out.println(decimalExample);
        System.out.println(signedPositiveExample);
        System.out.println(signedNegativeExample);
        System.out.println(radixExample);
        System.out.println(stringExample);
    }
}


Output

20
20
-20
32
11670324





Last Updated : 22 Dec, 2023
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