Tutorial by Examples



The toString() method is used to create a String representation of an object by using the object´s content. This method should be overridden when writing your class. toString() is called implicitly when an object is concatenated to a string as in "hello " + anObject. Consider the followin...
TL;DR == tests for reference equality (whether they are the same object) .equals() tests for value equality (whether they are logically "equal") equals() is a method used to compare two objects for equality. The default implementation of the equals() method in the Object class returns...
When a Java class overrides the equals method, it should override the hashCode method as well. As defined in the method's contract: Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, ...
wait() and notify() work in tandem – when one thread calls wait() on an object, that thread will block until another thread calls notify() or notifyAll() on that same object. (See Also: wait()/notify() ) package com.example.examples.object; import java.util.concurrent.atomic.AtomicBoolean; p...
The getClass() method can be used to find the runtime class type of an object. See the example below: public class User { private long userID; private String name; public User(long userID, String name) { this.userID = userID; this.name = name; } } pu...
The clone() method is used to create and return a copy of an object. This method arguable should be avoided as it is problematic and a copy constructor or some other approach for copying should be used in favour of clone(). For the method to be used all classes calling the method must implement the...
This is a protected and non-static method of the Object class. This method is used to perform some final operations or clean up operations on an object before it gets removed from the memory. According to the doc, this method gets called by the garbage collector on an object when garbage collecti...
All constructors in Java must make a call to the Object constructor. This is done with the call super(). This has to be the first line in a constructor. The reason for this is so that the object can actually be created on the heap before any additional initialization is performed. If you do not spe...

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