How to Convert an int to a String in Java

Turning an int into a String is one of the most common conversions in Java — you need it whenever you log a number, build a message, or write a value to a file. The JDK offers several ways to do it, and they all produce the same text. This chapter shows the idiomatic options and when to reach for each.

Integer.toString — the direct call

The clearest, most explicit way is Integer.toString(int). It says exactly what it does and returns the decimal text of the number:

int n = 256;
String s = Integer.toString(n); // "256"

This is the method String.valueOf and concatenation both end up calling internally, so it is the canonical conversion. Negative values keep their sign (Integer.toString(-7) returns "-7"), and the result is never null.

String.valueOf — null-safe and overloaded

String.valueOf is overloaded for every primitive type, so the same call works for int, long, double, boolean, and char:

int n = 256;
String s = String.valueOf(n); // "256"

For an int it simply delegates to Integer.toString, so the output is identical. Many developers prefer it because the single name covers all primitives and it is the conventional choice when converting an object reference that might be null (it returns "null" instead of throwing).

String concatenation — quick but watch the cost

Appending an int to an empty string forces a conversion:

int n = 256;
String s = "" + n; // "256"

It is concise and fine for a one-off, but the compiler turns it into a StringBuilder operation. Inside a loop, repeated "" + n builds many throwaway objects; prefer Integer.toString or a single StringBuilder there.

String.format and radix conversions

When you need padding, a sign, or a non-decimal base, use String.format or the radix-aware Integer methods:

String padded = String.format("%05d", 42);   // "00042"
String hex    = Integer.toString(255, 16);    // "ff"
String binary = Integer.toBinaryString(255);  // "11111111"

Here is how the everyday options compare:

A worked example

This program runs every approach on the same value, confirms the three common methods produce equal strings, and shows formatting and radix output.

What to take from the run:

• Integer.toString(-42), String.valueOf(-42), and "" + (-42) all print -42 — the three common ways are interchangeable for plain decimal text.
• The equal? line prints true, proving the three results are character-for-character identical, because String.valueOf and concatenation both route through Integer.toString.
• The negative sign survives the conversion, and the resulting string has length 3 (-, 4, 2) — the minus counts as a character.
• String.format("%05d", 42) prints 00042, showing how the %05d directive zero-pads to a minimum width of five.
• Integer.toBinaryString(255) prints 11111111 and Integer.toString(255, 16) prints ff, demonstrating that an int can be rendered in any base, not just decimal.

Practice