How to convert String to int in Java

In Java, we can use Integer.parseInt(String) to convert a String to an int; For unparsable String, it throws NumberFormatException.

  Integer.parseInt("1");      // ok
  Integer.parseInt("+1");     // ok, result = 1
  Integer.parseInt("-1");     // ok, result = -1
  Integer.parseInt("100");    // ok

  Integer.parseInt(" 1");     // NumberFormatException (contains space)
  Integer.parseInt("1 ");     // NumberFormatException (contains space)
  Integer.parseInt("2147483648"); // NumberFormatException (Integer max 2,147,483,647)
  Integer.parseInt("1.1");    // NumberFormatException (. or any symbol is not allowed)
  Integer.parseInt("1-1");    // NumberFormatException (- or any symbol is not allowed)
  Integer.parseInt("");       // NumberFormatException, empty
  Integer.parseInt(" ");      // NumberFormatException, (contains space)
  Integer.parseInt(null);     // NumberFormatException, null

1. Convert String to int

Below example uses Integer.parseInt(String) to convert a String “1” to a primitive type int.

ConvertStringToInt.java

package com.favtuts.string;

public class ConvertStringToInt {
    public static void main(String[] args) {

        String number = "1";
  
        // String to int
        int result = Integer.parseInt(number);
  
        // 1
        System.out.println(result);
  
    }
}

Output

1

2.How to handle NumberFormatException

2.1 For invalid number or unparsable String, the Integer.parseInt(String) throws NumberFormatException.

  String number = "1A";
  int result = Integer.parseInt(number); // throws NumberFormatException

Output

Exception in thread "main" java.lang.NumberFormatException: For input string: "1A"
	at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
	at java.base/java.lang.Integer.parseInt(Integer.java:668)
	at java.base/java.lang.Integer.parseInt(Integer.java:786)
	at com.favtuts.string.ConvertStringToInt.main(ConvertStringToInt.java:18)

2.2 The best practice is catch the NumberFormatException during the conversion.

ConvertStringToInt.java

package com.favtuts.string;

public class ConvertStringToInt {
    public static void main(String[] args) {       
  
        String number = "1A";
        try {
            int result = Integer.parseInt(number);
            System.out.println(result);
        } catch (NumberFormatException e) {
            //do something for the exception.
            System.err.println("Invalid number format : " + number);
        }
    }
}

Output

Invalid number format : 1A

3. Integer.MAX_VALUE = 2147483647

Be careful, do not convert any numbers greater than 2,147,483,647, which is Integer.MAX_VALUE; Otherwise, it will throw NumberFormatException.

ConvertStringToInt2.java

package com.favtuts.string;

public class ConvertStringToInt2 {
    
    public static void main(String[] args) {
        
        // 2147483647
        System.out.println(Integer.MAX_VALUE);

        String number = "2147483648";
        try {
            int result = Integer.parseInt(number);
            System.out.println(result);
        } catch (Exception e) {
            //do something for the exception.
            System.err.println("Invalid number format : " + number);
        }
    }
}

Output

2147483647
Invalid number format : 2147483648

4. Integer.parseInt(String) vs Integer.valueOf(String)

The Integer.parseInt(String) convert a String to primitive type int; The Integer.valueOf(String) convert a String to a Integer object. For unparsable String, both methods throw NumberFormatException.

  int result1 = Integer.parseInt("1");

  Integer result2 = Integer.valueOf("1");

Download Source Code

$ git clone https://github.com/favtuts/java-core-tutorials-examples

$ cd java-string

References

• Integer.parseInt​ JavaDoc 17
• NumberFormatException JavaDoc 17
• Java – Check if String is numeric
• Convert String to Integer in Java