How to Convert String to Int in Java

By Alexander Kurilo 11/23/2020 Java String 1 Comment

I think you will agree with me when I say:

Converting String to int in Java is a REALLY one of the most used operations.

I’ll show 10 methods of how to change String to int with descriptions and examples.

How to Convert a String to an Int in Java Methods Overview

If you need to parse String to primitive int – use Integer.parseInt
If you are sure that result is always positive and you should convert String to primitive int – use Integer.parseUnsignedInt
If you need to convert String to Integer object – use Integer.valueOf
If you have String in special format (“0x“, “0X“, “#“) – use Integer.decode
If you need to turn a string into an int and specify default value in case of NumberFormatException – use NumberUtils.toInt from apache.commons.lang

NOTE: It’s impossible to cast String object to primitive int or to Integer object. This code won’t compile. You should use methods described here to parse a string to int.

Integer.parseInt(s)

Converts a String value as a signed primitive int.

Method signature:

1	public static int parseInt(String s) throws NumberFormatException

Example:

1 2	int i = Integer.parseInt("100"); System.out.println(i);

Output:

100

Integer.parseInt(s, radix)

Parses a string argument as a signed primitive int in the radix specified by the second argument.

Method signature:

1	public static int parseInt(String s, int radix) throws NumberFormatException

Examples:

System.out.println(Integer.parseInt("0", 10));

System.out.println(Integer.parseInt("473", 10));

System.out.println(Integer.parseInt("+42", 10));

System.out.println(Integer.parseInt("-0", 10));

System.out.println(Integer.parseInt("-FF", 16));

System.out.println(Integer.parseInt("1100110", 2));

System.out.println(Integer.parseInt("2147483647", 10));

System.out.println(Integer.parseInt("-2147483648", 10));

System.out.println(Integer.parseInt("2147483648", 10));

System.out.println(Integer.parseInt("99", 8))

System.out.println(Integer.parseInt("Kona", 10));

System.out.println(Integer.parseInt("Kona", 27));

Output:

473

-255

102

2147483647

-2147483648

throws a NumberFormatException

411787

Since: Java 8

Integer.parseInt(s, beginIndex, endIndex, radix)

Turning a CharSequence value into a signed primitive int in the radix specified by the second argument from beginIndex to endIndex.

Note: The method has no protection against CharSequence mutation during parsing.

Method signature:

1	public static int parseInt(CharSequence s, int beginIndex, int endIndex, int radix) throws NumberFormatException

Examples:

String cssColor = "#4dba16";

int red = Integer.parseInt(cssColor, 1, 3, 16);

int green = Integer.parseInt(cssColor, 3, 5, 16);

int blue = Integer.parseInt(cssColor, 5, 7, 16);

System.out.println(red);

System.out.println(green);

System.out.println(blue);

int amount = Integer.parseInt("I have 2000$ on my bank account", 7, 11, 10);

System.out.println(amount);

Output:

186

2000

Since: Java 9

Integer.parseUnsignedInt(s)

Converts a String value to an unsigned primitive int.

Method signature:

1	public static int Integer.parseUnsignedInt(String s) throws NumberFormatException

Examples:

1 2	int i = Integer.parseUnsignedInt("2017"); System.out.println(i);

Integer.parseUnsignedInt(s, radix)

Parses a String argument as an unsigned primitive int in the radix specified by the second argument.

Method signature:

1	public static int parseUnsignedInt(String s, int radix) throws NumberFormatException

Examples:

int iDecimal = Integer.parseUnsignedInt("75", 10); // base 10 decimal

System.out.println("iDecimal = " + iDecimal);

int iOctal = Integer.parseUnsignedInt("011", 8); // base 8 octal

System.out.println("iOctal = " + iOctal);

int iHexadecimal = Integer.parseUnsignedInt("aC", 16); // base 16 hexadecimal

System.out.println("iHexadecimal = " + iHexadecimal);

Since: Java 8

Integer.parseUnsignedInt(s, beginIndex, endIndex, radix)

Turning a CharSequence value into an unsigned primitive int in the radix specified by the second argument from beginIndex to endIndex.

Method signature:

1	public static int parseUnsignedInt(CharSequence s, int beginIndex, int endIndex, int radix) throws NumberFormatException

Examples:

int result1 = Integer.parseInt("010010000100001001000100", 0, 7, 2);

System.out.println(result1);

int result2 = Integer.parseInt("-6B4A", 0, 3, 16);

System.out.println(result2);

int result2 = Integer.parseUnsignedInt("6B4A", 0, 3, 16);

System.out.println(result2);

Output:

-107

1716

Since: Java 9

Integer.valueOf(s)

Converts a String to an Integer object.

Method signature:

1	public static Integer.valueOf(String s) throws NumberFormatException

Example:

1 2	Integer i = Integer.valueOf("100"); System.out.println(i);

Output:

100

Integer.valueOf(s, radix)

Parses a String as an Integer object in the radix specified by the second argument.

Method signature:

1	public static Integer.valueOf(String s, int radix) throws NumberFormatException

Examples:

int binary = Integer.valueOf("11111111", 2);

System.out.println(binary);

int octal = Integer.valueOf("377", 8);

System.out.println(octal);

int hexadecimal = Integer.valueOf("ff", 16);

System.out.println(hexadecimal);

Output:

255

Since: Java 8

Integer.decode(s)

Decodes a String into an Integer. Accepts decimal, hexadecimal, and octal numbers in the following format:

Sign	Opt	Name	Examples
±		DecimalNumeral	555, -475
±	`0X`	HexDigits	0XA, -0X12A
±	`0x`	HexDigits	0xA, -0x12A
±	`#`	HexDigits	-#A, #123
±	`0`	OctalDigits	010, -010

Method signature:

1	public static Integer decode(String nm) throws NumberFormatException

Examples:

System.out.println("octal numbers: " + Integer.decode("010"));

System.out.println("hexadecimal numbers: " + Integer.decode("0XA"));

System.out.println("minus hexadecimal numbers: " + Integer.decode("-0XA"));

System.out.println("minus hexadecimal numbers: " + Integer.decode("-#A"));

Output:

octal numbers: 8

hexadecimal numbers: 10

minus hexadecimal numbers: -10

NumberUtils.toInt(s)

NumberUtils class contains some useful methods to parse strings. To Include it to the project you should add maven dependency:

<groupId>commons-lang</groupId>

<artifactId>commons-lang</artifactId>

</dependency>

and import org.apache.commons.lang3.math.NumberUtils to your class.

Method signature:

1	public static int NumberUtils.toInts(String s)

Example:

1 2	int i = NumberUtils.toInt("100"); System.out.println(i);

Output:

100

Implementation with a default value as a second argument would be useful if you’re not sure what’s inside of the input String and you want to provide a fallback value.

Method signature:

1	public static int NumberUtils.toInts(String s, int defaultValue)

Example:

If the string is null, the default value is returned.

System.out.println(NumberUtils.toInt("100"));

System.out.println(NumberUtils.toInt(null, 1));

System.out.println(NumberUtils.toInt("", 2));

System.out.println(NumberUtils.toInt("qwerty", 3));

Output:

100

Any questions? Please, ask me.

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About Author

Alexander Kurilo

I'm a beginner Java developer. I decided to share my experience of solving problems that a Java developer is facing.