TutorialsJava

Java - Convert String to int

To convert a String to int in Java, we can use:

Integer.parseInt()

int i1 = Integer.parseInt("101010101");
System.out.println(i1);  // 101010101

int i2 = Integer.parseInt("-8F", 16);
System.out.println(i2);  // -143

int i3 = Integer.parseInt("101010101", 2);
System.out.println(i3);  // 341

We also can use Integer.parseUnsignedInt​(...) to make sure the integer is > 0.

Integer.valueOf()

The difference between valueOf(...) and parseInt(...) is valueOf(...) will return an Integer (wrapper class) instead of primitive int.

  • static Integer valueOf(String s)​: Returns an Integer object holding the value of the specified String.
  • static Integer valueOf​(String s, int radix): Returns an Integer object holding the value extracted from the specified String when parsed with the radix given by the second argument.
int i1 = Integer.valueOf("101010101");
System.out.println(i1);  // 101010101

int i2 = Integer.valueOf("-8F", 16);
System.out.println(i2);  // -143

int i3 = Integer.valueOf("101010101", 2);
System.out.println(i3);  // 341

As you can see, implicit casting automatically unbox Integer into int.

Deprecated: Integer‘s Constructor

Integer(String s)​ is deprecated.

It is rarely appropriate to use this constructor. Use parseInt(String) to convert a string to a int primitive, or use valueOf(String) to convert a string to an Integer object.

int i1 = new Integer("888");
System.out.println(i1);  // 888

int i2 = new Integer("-0x8F");  // NumberFormatException
System.out.println(i2);

Integer.decode()

static Integer decode​(String nm): Decodes a String into an Integer.

int i1 = Integer.decode("888");
System.out.println(i1);  // 888

int i2 = Integer.decode("-0x8F");  // hex
System.out.println(i2);  // -143

int i3 = Integer.decode("#8F");  // hex
System.out.println(i3);  // 143

int i4 = Integer.decode("075");  // octal
System.out.println(i4);  // 61

DecimalFormat.parse()

parse​(String source) throws ParseException: Parses text from the beginning of the given string to produce a number. The method may not use the entire text of the given string.

import java.text.DecimalFormat;
import java.text.ParseException;

DecimalFormat decimalFormat = new DecimalFormat();
try {
    int i = decimalFormat.parse("51234").intValue();
    System.out.println(i);  // 51234
} catch (ParseException e) {
    System.out.println(e.getMessage());
}

Apache Commons NumberUtils

If using maven, you need to add commons-lang3 as your dependency.

<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.8.1</version>
</dependency>

and import:

import org.apache.commons.lang3.math.NumberUtils;

Methods:

int i1 = NumberUtils.toInt("888");
System.out.println(i1);  // 888

int i2 = NumberUtils.toInt(null);
System.out.println(i2);  // 0

int i3 = NumberUtils.toInt("888", 0);
System.out.println(i3);  // 888

int i4 = NumberUtils.toInt("xyz", 99);
System.out.println(i4);  // 99

int i5 = NumberUtils.toInt("", 99);
System.out.println(i5);  // 99

int i6 = NumberUtils.createInteger("888");
System.out.println(i6);  // 888

int i7 = NumberUtils.createInteger("-0x8F");
System.out.println(i7);  // -143

Spring NumberUtils

Make sure spring-core is added as your dependency:

<!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>5.1.2.RELEASE</version>
</dependency>

and import:

import org.springframework.util.NumberUtils;

Methods:

int i1 = NumberUtils.parseNumber("888", Integer.class);
System.out.println(i1); // 888

int i2 = NumberUtils.parseNumber("-0x8F", Integer.class);
System.out.println(i2);  // -143

parseNumber also built for another Number type, not only int/Integer.

Google Guava Ints.tryParse()

The conversion also can be done using Guava’s Ints.tryParse(). Add guava as one of our dependency:

<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>27.1-jre</version>
</dependency>

then import:

import com.google.common.primitives.Ints;

Methods:

int i1 = Ints.tryParse("101010101");
System.out.println(i1);  // 101010101

int i2 = Ints.tryParse("-8F", 16);
System.out.println(i2);  // -143

int i3 = Ints.tryParse("101010101", 2);
System.out.println(i3);  // 341

NumberFormatException

If the application has attempted to convert a string to one of the numeric types, but that the string does not have the appropriate format (or null/empty) , a NumberFormatException will be thrown.

int i = Integer.parseInt("-0x8F");
System.out.println(i);  // NumberFormatException
                    

Exception in thread "main" java.lang.NumberFormatException: For input string: "-0x8F"
	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 com.dariawan.string.StringToInt.main(StringToInt.java:66)

Check on How to Handle NumberFormatException in Java

My Take

My take is, I'm using Apache Commons NumberUtils.toInt(...). It's able to handle NumberFormatException, and returning default value (or 0)

This article is part of Java String With Examples Series.

Other articles in this series:

Published 27 March 2019

Desson Ariawan

Desson AriawanProgrammer

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