The toString method is defined in the java.lang.Object class and returns the object class name and its internal address:
public String toString() { return getClass().getName() + "@" + Integer.toHexString(hashCode()); }
The java.util.Objects class provides utility methods to get the string value code of an object:
public static String toString(Object o) { return String.valueOf(o); }
public static String toString(Object o, String nullDefault) { return (o != null) ? o.toString() : nullDefault; }
The java.util.Arrays class provides utility methods to get the string value of an array of objects (including specific overloaded methods for each primitive type). It also provides a utility method to get a deep string value of an array of objects (array of arrays).

The following is a sample code that show how to implement the toString method.

• Superclass "P":
  class P { Integer id = 1; @Override public String toString() { String value = "%s@%X (id:%d)"; return String.format(Locale.getDefault(), value, getClass().getName(), System.identityHashCode(this), id); } }
  
• Subclass "C":
  class C extends P { String code = "default"; @Override public String toString() { String value = "%s (code:%s)"; return String.format(Locale.getDefault(), value, super.toString(), code); } }