When to Use toString vs String.valueOf vs Casting in Java? A Practical Guide

1. Introduction

In daily development you often encounter three ways to convert objects to strings in Java: toString(), String.valueOf(), and casting (String). This article explains when to use each method.

2. Code Examples

1. Primitive Types

(1) Primitive types have no toString() method

(2) Recommended usage

(3) Cannot cast directly

(String) is a standard type conversion; when using (String) casting, it is advisable to check with instanceof to avoid ClassCastException. The compiler does not warn about syntax errors, so use cautiously.

2. Wrapper Types

(1) toString() works

(2) String.valueOf()

Also works.

(3) Wrapper types cannot be cast directly

3. Null Value Issues

(1) toString() throws NullPointerException

(2) String.valueOf() returns the string "null"

(3) Casting null succeeds

3. Source Code Analysis

1. toString()

2. String.valueOf()

String.valueOf() adds a null check compared to toString().

4. Conclusion

1. toString()

May throw NullPointerException if the object is null; subclasses usually override it.

2. String.valueOf()

Recommended because it avoids NullPointerException and returns the string "null" for null values.

3. (String) casting

Standard conversion but should be used with instanceof checks to prevent ClassCastException.