How do I convert from int to String?

java

string-conversion

java-8

best-practices

byNikita Barsukov·Sep 19, 2024

To convert an int to a String in Java, use the String.valueOf(int) method:

// Fast, easy and no fuss!
String str = String.valueOf(123);

Alternatively, you could concatenate the integer with an empty String:

// Not the best method, but it does work!
String str = 123 + "";

Understanding int to String conversion

String.valueOf(int) and integer concatenation are two simple ways to convert from int to String. String.valueOf(int) is a method provided by the Java String class, designed to convert primitive data types to String.

On the other hand, concatenating an integer with an empty string does work, but under the hood, it's using StringBuilder to achieve it. While this won't impact performance for standalone conversions, it can be less efficient in loops or when dealing with large data.

Exploring conversion methods and considerations

Leverage String.format

String.format is the go-to method when you need to format the integer or integrate it into a more complex string structure:

// Format integers like a pro!
String str = String.format("%d", 123);

Avoid common pitfalls

While concatenating an integer with an empty string may seem convenient, it can create confusion and hinder code readability. Using Integer.toString(int) instead clearly signals your intent to convert an int to a String.

Improve conversion skills

Mastering Java conversions requires knowing when and why to use different methods. Although concatenating an integer with an empty string is quick-fix, using best practices like Integer.toString(int) or String.valueOf(int) will lead to cleaner and more efficient code.

Conversions that care about format

You might need your integer to have a specific format when converted to a string, e.g., zero-padding or comma as thousand separator. String.format serves this purpose perfectly:

// Look, mom! No leading zeroes!
String padded = String.format("%05d", 123); 
// Money, money, money...
String withCommas = String.format("%,d", 123456);

Considering StringBuilder

Understanding when to use StringBuilder is crucial for managing strings, especially within loops. Here's an example:

// StringBuilder - once your friend, always your friend!
StringBuilder sb = new StringBuilder();
for(int i = 0; i < 10; i++) {
    sb.append(i);
}
String sequence = sb.toString();