1. Using Integer.parseInt() Method in Java
The first function that we use to convert java string to int is Integer.parseInt(). The string is returned as an int primitive type when we use this. Let's see an example code that will convert java string to int.
Syntax of parseInt
int number = Integer.parseInt(String s);
Parameters
- s: The String to be parsed into an integer.
Return Type
- int: The method returns an integer representation of the String. If the string cannot be parsed as an integer, a NumberFormatException is thrown.
We can see that compiler is giving is error. You can try it on online java compiler.
Cases of parseInt() Method
The parseInt() method in Java is used to convert a String into an integer. This method is commonly used when parsing numbers from user input, configuration files, or other data sources that provide numeric values as strings. The method can handle both positive and negative numbers, and it also allows for specifying a radix (e.g., binary, octal, decimal, hexadecimal) when parsing the string.
Number Format Exceptions of parseInt() Method
A NumberFormatException occurs when the parseInt() method is unable to convert the provided String into an integer due to invalid format or characters.
Example:
public class ParseIntExample {
public static void main(String[] args) {
try {
int number = Integer.parseInt("123abc");
} catch (NumberFormatException e) {
System.out.println("NumberFormatException: " + e.getMessage());
}
}
}
You can also try this code with Online Java Compiler
Explanation:
In this example, the string "123abc" contains non-numeric characters (abc), causing the parseInt() method to throw a NumberFormatException. The exception indicates that the string cannot be parsed as an integer.
2. Using Integer.valueOf() Method
Another approach to converting a String to an integer in Java is by using the valueOf() method. This method also belongs to the Integer class and works similarly to parseInt(). However, it returns an Integer object instead of a primitive int.
Syntax:
Integer.valueOf(String s);
Example:
Integer number = Integer.valueOf("123");
Explanation:
The valueOf() method converts the string "123" into an Integer object. This approach is useful when you need to work with Integer objects instead of primitive int values. If the string cannot be converted, a NumberFormatException will also be thrown.
Let's see an example code that will convert java string to int.
string s="69";
Integer integer = integer.valueOf(str);
System.out.println(integer);
Note: Similar to Integer.parseInt() A NumberFormatException will be thrown if the string does not include a valid number.
As a result, we must handle this exception every time we convert java string to int by placing the code within the try-catch block. Let's see the example and see the error that we will receive when we try to convert java string to int, which contains invalid input.
string s = "69P";
try
{
Integer integer = integer.valueOf(str);
System.out.println(integer);
}
catch (NumberFormatException ex)
{
ex.printStackTrace();
}
Output
java.lang.NumberFormatException: For input string: "69P"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.valueOf(Integer.java:766)
at OOP.StringTest.main(StringTest.java:42)
Frequently Asked Questions
Why do we need to convert string to int in java?
The first question that will come to your mind is why we should convert java string to int. It is commonly used when doing mathematical operations on a string containing a number. The entered data is received as a string whenever we get data from TextField or TextArea. We must convert the java string to int if the provided data is in numerical format..
What is the difference between Integer.valueOf() and Integer.parseInt()?
Integer.valueOf() returns an Integer object, while Integer.parseInt() returns a primitive int. Additionally, Integer.valueOf() caches values between -128 and 127, improving performance, whereas parseInt() always returns a primitive int.
What is the Integer.valueOf() in Java?
Integer.valueOf() converts a string or int into an Integer object and uses caching for better performance with frequently used values.
What is parseInt() in Java?
Integer.parseInt() converts a valid numeric string into a primitive int value and throws a NumberFormatException for invalid inputs.
How to convert string to integer without using any direct method in Java?
You can convert a string to an integer manually by iterating through each character, calculating its numeric value using ASCII, and adjusting for place values, effectively performing the conversion algorithmically without built-in methods.
What will happen if the String cannot be converted to an int?
If the string cannot be converted to an int, both Integer.parseInt() and Integer.valueOf() will throw a NumberFormatException, indicating the string is not a valid integer representation.
Conclusion
Converting a String to an int in Java is a fundamental operation that is crucial for handling user input, data processing, and other tasks where numerical data is represented as text. The parseInt() method is a straightforward and widely used approach for this conversion, but it must be used carefully to avoid NumberFormatException errors when dealing with improperly formatted strings.
Recommended Readings:
27+ registered 
