Differences between String.valueOf(Object) and Object.toString() are:

1) If string is null,

String.valueOf(Object) will return "null", whereas Object::toString() will throw a null pointer exception.

public static void main(String args[]){  
    String str = null;
    
    System.out.println(String.valueOf(str));  // it will print null        
    System.out.println(str.toString()); // it will throw NullPointerException        
}  

2) Signature:

valueOf() method of String class is static. whereas toString() method of String class is non static.

The signature or syntax of string's valueOf() method is given below:

public static String valueOf(boolean b)  
public static String valueOf(char c)  
public static String valueOf(char[] c)  
public static String valueOf(int i)  
public static String valueOf(long l)  
public static String valueOf(float f)  
public static String valueOf(double d)  
public static String valueOf(Object o)

The signature or syntax of string's toString() method is given below:

public String toString()