{"id":43667,"date":"2015-09-18T21:43:46","date_gmt":"2015-09-18T18:43:46","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=43667"},"modified":"2023-12-06T12:37:36","modified_gmt":"2023-12-06T10:37:36","slug":"using-methods-common-to-all-objects","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2015\/09\/using-methods-common-to-all-objects.html","title":{"rendered":"Using methods common to all objects"},"content":{"rendered":"

This article is part of our Academy Course titled Advanced Java<\/a>.<\/p>\n

This course is designed to help you make the most effective use of Java. It discusses advanced topics, including object creation, concurrency, serialization, reflection and many more. It will guide you through your journey to Java mastery! Check it out here<\/a>!<\/em><\/p>\n

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Table Of Contents<\/h4>\n
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1. Introduction<\/a><\/dt>\n
2. Methods equals and hashCode<\/a><\/dt>\n
3. Method toString<\/a><\/dt>\n
4. Method clone<\/a><\/dt>\n
5. Method equals and == operator<\/a><\/dt>\n
6. Useful helper classes<\/a><\/dt>\n
7. Download the Source Code<\/a><\/dt>\n
8. What’s next<\/a><\/dt>\n<\/dl>\n<\/div>\n

<\/a>1. Introduction<\/h2>\n

From part 1<\/strong> of the tutorial, How to create and destroy objects<\/a><\/strong>, we already know that Java is an object-oriented language (however, not a pure object-oriented one). On top of the Java class hierarchy sits the Object<\/a><\/code> class and every single class in Java implicitly is inherited from it. As such, all classes inherit the set of methods declared in Object<\/code>class, most importantly the following ones:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Method<\/strong><\/td>\nDescription<\/strong><\/td>\n<\/tr>\n
protected Object clone()<\/code><\/td>\nCreates and returns a copy of this object.<\/td>\n<\/tr>\n
protected void finalize()<\/code><\/td>\nCalled by the garbage collector on an object when garbage collection determines that there are no more references to the object. We have discussed finalizers in the part 1<\/strong> of the tutorial, How to create and destroy objects<\/strong>.<\/td>\n<\/tr>\n
boolean equals(Object obj)<\/code><\/td>\nIndicates whether some other object is \u201cequal to\u201d this one.<\/td>\n<\/tr>\n
int hashCode()<\/code><\/td>\nReturns a hash code value for the object.<\/td>\n<\/tr>\n
String toString()<\/code><\/td>\nReturns a string representation of the object.<\/td>\n<\/tr>\n
void notify()<\/code><\/td>\nWakes up a single thread that is waiting on this object’s monitor. We are going to discuss this method in the part 9<\/strong> of the tutorial, Concurrency best practices<\/strong>.<\/td>\n<\/tr>\n
void notifyAll()<\/code><\/td>\nWakes up all threads that are waiting on this object’s monitor. We are going to discuss this method in the part 9<\/strong> of the tutorial, Concurrency best practices<\/strong>.<\/td>\n<\/tr>\n
void wait()<\/code>, void wait(long timeout)<\/code>, void wait(long timeout, int nanos)<\/code><\/td>\nCauses the current thread to wait until another thread invokes the notify()<\/code> method or the notifyAll()<\/code> method for this object. We are going to discuss these methods in the part 9<\/strong> of the tutorial, Concurrency best practices<\/strong>.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Table 1<\/p>\n<\/div>\n

In this part of the tutorial we are going to look at equals<\/code>,hashCode<\/code>,toString<\/code> and clone<\/code> methods, their usage and important constraints to keep in mind.<\/p>\n

<\/a>2. Methods equals and hashCode<\/h2>\n

By default, any two object references (or class instance references) in Java are equal only if they are referring to the same memory location (reference equality). But Java allows classes to define their own equality rules by overriding the equals()<\/code> method of the Object<\/code> class. It sounds like a powerful concept, however the correct equals()<\/code> method implementation should conform to a set of rules and satisfy the following constraints:<\/p>\n