To convert Java String to Int is one of the commonly used operation in the Java programs. There are 8 methods available to perform this conversion.
You can convert Java String to Int using Integer.parseInt() method or Integer.valueOf() method.
In this tutorial, you’ll learn
- Java APIs available to convert
StringtointorInteger - External Libraries available to convert
StringtoInt - When to use the different methods
- Exceptions to be handled
The recommended method to convert String to int is using the Java API itself as given below.
try {
final int result = Integer.parseInt(numAsString);
System.out.println("String converted to number using Integer.parseInt : " + result);
} catch (final NumberFormatException e) {
System.err.println("Unable to convert String " + numAsString
+ " to int. A NumberFormatException Occured, Ensure the string contains only valid numbers " + e);
}Read the below detailed methods to understand how to convert Java String to int using various methods available and when its appropriate to use each method.
Using Integer.parseInt()
You can easily convert String to Int in java using the Integer.parseInt() method available by default in Java.
There are two overloaded methods available in Integer.parseInt() as explained below
Integer.parseInt(String Str)
Integer.ParseInt(String str) accepts only a String which needs to be converted to int.
When to Use
Use this method when you want to convert a String which has only numbers and a default radix shall be used to convert.
Points to Note
The leading zeros will be ignored when converting String to int using the parseInt() method.
If you want to preserve the leading zeros, then do not use this method.
Snippet
The below is the code snippet to convert the string to int.
final int result = Integer.parseInt(numAsString);Returns
A primitive int type representing the String.
Exceptions to Handle
The Integer.parseInt() throws the NumberFormatException in the following cases.
- If the
Stringisnullor Empty. - If the
Stringis not a parse-able integer. For e.g., it contains any characters other than numbers. Except the – sign which can be used to denote a negative number.
Using Integer.parseInt(String) to Convert With Leading Zeros
If you want to convert String to int with leading zeros, then use the below code snippet.
%05d in the string format method specifies, 5 digit leading zeros should be preserved.
public static void main(String args[]){
String str="0000077";
str = String.format("%05d", Integer.parseInt(str));
System.out.println("Output String: "+str);
}Integer.parseInt(String Str, Int Radix)
Integer.parseInt(String str, int radix) accepts a String to be converted to int and a radix to convert the String to a specific radix.
When to Use
You can use this method if you want to convert a String to int with specified Radix.
Code snippet
The below code is used to convert the String to int in the specified Radix.
final int result = Integer.parseInt(numAsString,10);Returns
A primitive int type representing the String.
Exceptions to Handle
The Integer.parseInt() throws the NumberFormatException in the following cases.
- If the
Stringisnullor Empty. - If the
Stringis not a parse-able integer. For e.g., it contains any characters other than numbers. Except the – sign which can be used to denote a negative number.
Example Program
Below example shows how to use the Integer.parseInt() with NumberFormatException.
private static void convertUsingParseInt() {
final String numAsString = "-500";
try {
final int result = Integer.parseInt(numAsString);
System.out.println("String converted to number using Integer.parseInt : " + result);
} catch (final NumberFormatException e) {
System.err.println("Unable to convert String " + numAsString
+ " to int. A NumberFormatException Occured, Ensure the string contains only valid numbers " + e);
}
}Using Integer.valueOf()
You can easily convert String to Integer in Java using the Integer.valueof() method. This can be used to convert Java string to Integer without parseInt() method.
There are two overloaded methods available as explained below.
Using Integer.valueOf(String S)
Integer.valueOf(String s) accepts only a String object to be converted to Integer.
When to Use
You can use this method, if you want to convert String to an Integer Object rather than the primitive int.
Returns
Returns Integer object representing the String.
If the Integer object is already available in the cache, then it returns the cached object.
Else it returns the new Integer object.
Code snippet
Below Snippet is used to convert to the String to Integer using valueOf().
final int result = Integer.valueOf(numAsString);Exceptions to Handle
NumberFormatException will be thrown by Integer.valueOf(String s) in following scenarios.
- If the
Stringis null or empty - If the
Stringcontains any characters other than integers. Except the ‘-‘ sign which can be used to denote the negative number.
Example Program
The below example shows how to convert String to Integer using the valueOf() method.
/**
*
*/
private static void convertUsingValueOf() {
final String numAsString = "500";
try {
final int result = Integer.valueOf(numAsString);
System.out.println("String converted to number using Integer.valueOf : " + result);
} catch (final NumberFormatException e) {
System.err.println("Unable to convert String " + numAsString
+ " to int. A NumberFormatException Occured, Ensure the string contains only valid numbers " + e);
}
}Using Apache Commons Lang3
Apache Commons Lang is a provides lot of helper methods for Java.lang API, especially String manipulations, Number conversions, objects reflections etc.
Latest Commons Lang3 Version: 3.11
You can download the binaries of the Commons Lang from this link.
Here is the download home page to get the other format of the binaries.
Pom File
To add commons lang as a dependency in Maven project, add the below code to your POM file.
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.12.0</version>
</dependency>Gradle Location
implementation group: 'org.apache.commons', name: 'commons-lang3', version: '3.12.0'You can use the toInt() available in the NumberUtils class of Commons lang API.
Now, you’ll see how to use the two different NumberUtils.toInt() to perform the convert operation.
NumberUtils.toInt(String Str)
NumberUtils.toInt(String str) accepts only the String object that will be converted to int.
This can be used to convert Java string to int without exception and it is null safe.
When to Use
Use if you do not want to handle any exception explicitly.
Returns
int represented by the String object.
0 – if the conversion fails due to any error or exception.
Code snippet
Use the below snippet to convert to String to int using toInt().
final int result = NumberUtils.toInt(numAsString);Exceptions to Handle
No exceptions to Handle as it returns 0 in case of exceptions.
Example Program
The below example shows how to convert String to Integer using the toInt() method.
/**
*
*/
private static void convertUsingValueOf() {
final String numAsString = "500";
final int result = NumberUtils.toInt(numAsString);
System.out.println("String converted to number using NumberUtils.toInt() : " + result);
}Using NumberUtils.toInt(String Str, Int defaultValue)
NumberUtils.toInt(String str, int defaultValue) accepts the String object that will be converted to int and a default value which should be returned in case if the conversion fails.
This can be used to convert Java string to int without exception and it is null safe.
When to Use
Use if you want to use any default value in case of failed conversion.
Returns
int represented by the string object, if the conversion is successful.
Default value, if the conversion fails due to any Exception.
Code snippet
Use the below snippet to convert to the String to int using toInt().
final int result = NumberUtils.toInt(numAsString,1);Exceptions to Handle
No exceptions to Handle as it returns the defaultValue in case of exceptions.
Example Program
The below example shows how to convert String to int using the toInt() method.
/**
*
*/
private static void convertUsingtoInt() {
final String numAsString = "500";
final int result = NumberUtils.toInt(numAsString, 1);
System.out.println("String converted to number using NumberUtils.toInt() : " + result);
}Using isDigit() and parseInt()
In this section, you’ll use the user defined function isDigit() to check if the given String is a proper number which can be converted to int or if it contains any characters which cannot be converted to int or Integer object.
This can also be used to convert Java string to int without exception.
If its a proper digit, then you can use parseInt() method available in the Integer class to convert String to Int primitive type and it is null safe.
When to Use
Use if
- You want to check if the string is a proper number before converting.
- You do not want to handle
NumberFormatExceptionin your program.
Example Program
In the below example class name StringtoIntExamples, isDigit() method is used to check if its a convertible String and then convert to int.
public class StringtoIntExamples {
public static void main(final String[] args) {
convertUsingParseInt();
}
/**
* @param input
* @return
*/
public static boolean isDigit(final String inputString) {
// input is null or an Empty String, return false.
if (inputString == null || inputString.isEmpty())
return false;
if (inputString.startsWith("-"))
// negative number in string, cut the first char
return inputString.substring(1).matches("[0-9]*");
else
// positive number return true for converting to int
return inputString.matches("[0-9]*");
}
/**
* Method to convert Java String to int using Integer parseInt.
*/
private static void convertUsingParseInt() {
String number = "-100";
if (isDigit(number)) {
System.out.println(Integer.parseInt(number));
}
else {
System.out.println("Please provide a String containing only numbers");
}
}Using Java 8 Optional and Streams
In this section, you’ll learn how to use Java8 Optional() and Streams to convert String to int.
Optional is a container object in java which may or may not contain values. This can be used when you want to avoid null check of any objects.
Streams are Classes which supports functional-style operations on streams of elements, such as map-reduce transformations on collections.
This is null safe method.
Snippet
final Optional<Integer> result = Optional.ofNullable(number).filter(StringtoIntExamples::isDigit)
.map(Integer::parseInt);where
- Optional.ofNullable(number) – Checks if the
Stringisnullor not - filter(StringtoIntExamples::isDigit) – Checks if the
Stringis a proper digit. Uses theisDigit()user defined method available in theStringtoIntExamplesclass. - map(Integer::parseInt) – Converts the
Stringtointusing theInteger.parseInt()usingStreams.
Example
If the String is not null, and a proper number means, then the resultant Optional object will return true when checked with isPresent().
If true then, return the number. Else display appropriate message to user.
/**
* Method to convert Java String to int using Java 8 optional.
*/
private static void convertUsingOptional() {
final String number = "10";
final Optional<Integer> result = Optional.ofNullable(number).filter(StringtoIntExamples::isDigit)
.map(Integer::parseInt);
if (result.isPresent())
System.out.println(result.get());
else
System.out.println("Please provide a valid digit [0-9]");
}This is how you can use Java8 Optional and Stream to convert String to Integer.
Using Google’s Guava Library
Google has a java core library called Guava with multiple utility methods and additional collection types.
You can use the tryParse() method available Ints class of Guava library to convert String to int without exception in case of problems.
Latest Google Guava Version: 30.1.1
You can download the binaries of the Google Guava from this link.
Here is the download home page to get the other format of the binaries.
Pom File
To add commons lang as a dependency in Maven project, add the below code to your POM file.
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>30.1.1-jre</version>
<!-- or, for Android: -->
<version>30.1.1-android</version>
</dependency>Gradle Location
dependencies {
// Pick one:
// 1. Use Guava in your implementation only:
implementation("com.google.guava:guava:30.1.1-jre")
// 2. Use Guava types in your public API:
api("com.google.guava:guava:30.1.1-jre")
// 3. Android - Use Guava in your implementation only:
implementation("com.google.guava:guava:30.1.1-android")
// 4. Android - Use Guava types in your public API:
api("com.google.guava:guava:30.1.1-android")
}Using tryParse(String Str)
tryParse(String str) parses the string into a signed decimal Integer value. This method accepts only ascii digits and the + ascii sign is rejected by default.
When to Use
You can use this method, if you want to avoid validation if the string is a valid number.
It is also null safe.
Returns
- Number representing the String
Code snippet
Integer result = Ints.tryParse(givenString);Exceptions to Handle
No exception needs to be handled explicitly. It returns null if there is a problem during conversion.
Example Program
/**
*
*/
private int void convertUsingtoInt(String numAsString) {
final int result = Ints.tryParse(numAsString);
System.out.println("String converted to number using NumberUtils.toInt() : " + result);
return result;
}Using Integer.decode()
Integer.decode() works similar to Integer.valueOf() but accepts different representations such as decimal, hexadecimal and octal numbers.
When to Use
Use when you want to convert a String with decimal, hexadecimal or octal number representations.
Returns
intrepresented by theString
Code snippet
int result = Integer.decode("500");Exceptions to Handle
NumberFormatException will be thrown by Integer.decode(String s) in following scenarios.
- If the
Stringis null or empty - If the
Stringcontains any characters other than integers. Except the ‘-‘ sign which can be used to denote the negative number.
Conclusion
String to int conversion is one of the commonly used operation when handling lot of user inputs. With Java evolving continuously, there are number of methods available to convert String to int or String to Integer object.
In this tutorial, You’ve learnt all the methods available to convert String to int in Java.
Feel free to comment if you have any questions or feedback.