String.valueOf() vs. Object.toString() in Java: Key Differences Explained

What are the differences between String.valueOf(Object) and Object.toString() in Java, and is there a specific code convention for using these methods?

String obj = null;
String str1 = String.valueOf(obj); // returns 'null'
String str2 = obj.toString(); // Throws NullPointerException

In Java, both String.valueOf(Object) and Object.toString() are used to convert an object to its string representation, but they exhibit different behaviors when handling null values and have distinct use cases.

// Example of using String.valueOf:
Object obj1 = null;
String result1 = String.valueOf(obj1); // result1 is 'null'

// Example of using Object.toString():
Object obj2 = new Object();
String result2 = obj2.toString(); // result2 is the object's memory address or a specific overridden string.

Causes

• String.valueOf(Object) gracefully handles null values by returning the string 'null'.
• Object.toString() can throw a NullPointerException if invoked on a null object reference.

Solutions

• Use String.valueOf(Object) when there's a possibility of the object being null to avoid runtime exceptions.
• Call Object.toString() when you are certain the object reference is not null and you want the object's string representation.

Mistake: Using Object.toString() on a null reference without checking.

Solution: Always ensure the object is not null before calling toString() or use String.valueOf() to prevent a NullPointerException.

Mistake: Assuming String.valueOf() behaves the same as toString() for non-null objects.

Solution: While both provide string representations, String.valueOf() is safer in scenarios where null could be involved.