What is parseInt in Java?

parseInt in Java

When you’re working with Java, you’ll often find yourself needing to convert text into numbers. This is where parseInt comes into play. But what is parseInt? Let’s break it down!

What is parseInt() in Java?

In Java, parseInt is a method used to convert a string into a whole number (an integer). For example, if you have a number written as text like “123”, and you want to use it in calculations, parseInt helps turn that text into a real number (123).

If the text isn’t a proper number, like “hello”, it will cause an error because “hello” can’t be turned into a number. This method is part of the Integer class, which provides several methods for dealing with integers. It is really handy when you get a number in the form of text, maybe from a file or a website, and you need to do math with it in your Java program.

Parameters of parseInt() in Java 

Single Parameter

  • String: This version of the method takes a single string parameter. The string should represent a valid integer value. For example, parseInt(“123”) will return the integer 123. If the string is not a valid integer, like “hello”, it will throw an error called NumberFormatException.

Two Parameters

  • String: Just like in the single-parameter version, this is the string that represents the integer you want to convert.
  • Radix: This is an optional second parameter that specifies the base of the number system used in the string. For example, if you use a radix of 2, the method will treat the string as a binary number. So parseInt(“101”, 2) will return the integer 5, because 101 is 5 in binary. If you don’t specify this parameter, the default is 10, which is the decimal system.

Java Integer parseInt() Method

1- Java Integer parseInt (String s) Method

This is the simplest form of the parseInt method. It takes a string (like “100”) and converts it into an integer (100). If the string does not represent a valid number, it will cause an error, known as a NumberFormatException.

2- Java Integer parseInt (String s, int radix) Method

This version of parseInt is similar to the first. However, it allows you to specify the number system (or radix) of the string you’re converting. For example, if you have a binary number in a string and you want to convert it to an integer, you would use a radix of 2. So, parseInt(“101”, 2) would return the integer 5, because 101 in binary is 5 in decimal.

3- Java Integer parseInt (CharSequence s, int beginText, int endText, int radix)

This method is a bit more advanced. It lets you convert a part of a string into an integer. The CharSequence is the type of the string you are working with, and you can specify where in the string to start (beginIndex) and where to end (endIndex). The radix works the same way as in the previous method, letting you define the number system. For example, if you have a string like “abc123def” and you only want to convert “123”, you would call parseInt(“abc123def”, 3, 6, 10) to focus on converting the part from index 3 to 6, using decimal (10) as the number system.

Return Values of parseInt() in Java 

Here’s what you need to know about the return values of parseInt() in Java:

  • Correct Conversion: If the string is a valid representation of an integer, like “123”, then parseInt() will return the integer value of that string, which in this case would be 123.
  • Leading and Trailing Spaces: The function can handle spaces before or after the number. So, if the string is ” 123 ” or ” 123″, parseInt() still returns the integer 123.
  • Invalid Strings: If the string does not contain a valid integer (like “abc”, “123abc”, or just an empty string “”), the function will not work properly. It will throw a NumberFormatException (a type of error indicating that the conversion could not be performed because the string does not format correctly as a number).
  • Partial Strings: For strings that start with numbers but are followed by non-numeric characters (like “123abc”), it throws a NumberFormatException as well. Only the initial characters can be converted if they are all digits.

Compatibility and Examples of parseInt in Java

parseInt() has been available since Java 1.0, making it compatible with all versions of Java. It’s a method in the Integer class, which is part of the core Java library. Here’s are some examples of parseInt in Java:

  • The most common use of parseInt() is to convert a string that represents a decimal number into an integer. If the string is something like “123”, using parseInt(“123”) will give you the integer 123.
  • Java allows you to specify a “radix” (the base of the number system) when converting strings to integers. For instance, if you have a binary number in a string, you can convert it using parseInt(“1010”, 2) to get the integer 10, since 1010 in binary equals 10 in decimal.
  • If you try to convert a string that has non-numeric characters (like “123abc”), parseInt() will throw a NumberFormatException because “123abc” isn’t a valid number in any numeral system. Similarly, if you pass a null string or use an invalid radix (outside the range of 2 to 36), you’ll also encounter errors.

Integer.valueOf() VS Integer.parseInt() with Examples

Aspect  Integer.parseInt() Integer.valueOf()
Return Type Returns a primitive int value. Returns an Integer object.
Parameter Type Accepts only String parameters. Accepts String, int, or char parameters.
Error with Char Parameter Throws an error if a char is passed as a parameter. Returns the ASCII value of the char passed.
Performance Generally faster when converting Strings to int. May be more efficient due to caching common values.
Usage Example int num = Integer.parseInt(“123”); Integer num = Integer.valueOf(“123”);

Troubleshooting Common Issues with ParseInt in Java

When you’re using Java’s parseInt() method, you might run into some issues, especially if the string you’re trying to convert into an integer isn’t quite right. Here’s how to handle two common problems:

Dealing with NumberFormatException

This error happens when Java tries to turn a string into an integer but finds something it doesn’t expect. This could be because:

  • The string is empty or null.
  • There are letters or symbols mixed in with the numbers.
  • There’s whitespace around the numbers that hasn’t been removed.

Here’s how you can handle it:

  • Always check the string before you try to parse it. Make sure it’s not null or empty.
  • Use trim() to remove any extra spaces from the beginning and end of the string.
  • If you expect non-numeric characters might be mixed in, remove them first or check if the string is purely numeric.

Handling Non-Numeric Strings

If your string might have letters or other non-numeric characters mixed in, and you only want the numbers, you need to clean up the string first:

  • You can use the replaceAll() method to keep only digits. For instance, input.replaceAll(“\\D+”, “”) changes “abc123def” into “123”.

Java’s String and Integer Classes

1- The String Class

In Java, the String class is used to handle text data. It’s a sequence of characters, like words or sentences. Strings in Java are immutable, which means once astring is created, its content can’t be changed. When you modify a string, Java actually creates a new string with the changes instead of altering the original. This makes strings safe from changes and easier to handle in multi-threaded environments where multiple threads might be accessing the same string. Common operations you can perform with the String class include:

  • Comparing two strings to see if they are the same.
  • Searching for a particular character or substring within a string.
  • Extracting a part of the string.
  • Converting the entire string to upper or lower case.

2- The Integer Class

The Integer class wraps a value of the primitive type int in an object. This class provides several helpful methods to manipulate integers. Like String, Integer objects are immutable. Once you create an Integer object, the value it holds cannot be changed. Some useful features of the Integer class include:

  • Converting an integer to a string and vice versa.
  • Comparing two integers.
  • Converting values from different bases (like binary or hexadecimal) to an integer.
  • Additionally, Integer class helps in handling integers as objects when needed for collections like ArrayList, which can only store objects, not primitive types.


To wrap up, parseInt in Java is a handy method for converting strings to integers. Understanding how to use this function effectively can save you a lot of trouble in managing input data and performing mathematical operations in your programs. 


What is parseInt() in Java?

  • parseInt() is a method in Java used to convert a string into an integer.
  • It helps in converting textual numeric data into actual numeric values usable in calculations.
  • This method is essential for handling user inputs and external data sources where numbers are represented as strings.

How does parseInt() handle non-numeric strings?

  • If the string passed to parseInt() is not a valid numeric representation, it throws a NumberFormatException.
  • Non-numeric characters, leading or trailing spaces, or empty strings cause this exception.
  • To avoid this, always ensure the string contains only valid numeric characters before using parseInt().

What are the parameters of the parseInt() method?

  • The simplest form of parseInt() takes a single parameter, the string to convert to an integer.
  • Another version accepts two parameters: the string to convert and the radix, specifying the number system of the string.
  • An advanced version allows converting a specific part of a string into an integer, with additional parameters for substring indices.

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