Java - no_image

Object class methods

Comparable	Comparator
public final Class getClass()	Returns the Class class object of this object. The Class class can further be used to get the metadata of this class.
public int hashCode()	Returns the hashcode number for this object.
public boolean equals(Object obj)	Compares the given object to this object.
protected Object clone()	Creates and returns the exact copy (clone) of this object.
public String toString()	Returns the string representation of this object.
public final void notify()	Wakes up single thread, waiting on this object’s monitor.
public final void notifyAll()	Wakes up all the threads, waiting on this object’s monitor.
public final void wait()	Causes the current thread to wait, until another thread notifies (invokes notify() or notifyAll() method).
public final void wait(long timeout)	Causes the current thread to wait for the specified milliseconds, until another thread notifies (invokes notify() or notifyAll() method).
public final void wait(long timeout,int nanos)	Causes the current thread to wait for the specified milliseconds and nanoseconds, until another thread notifies (invokes notify() or notifyAll() method).

getClass()

You cannot override getClass. The getClass() method returns a Class object, which has methods you can use to get information about the class, such as its name (getSimpleName()), its superclass (getSuperclass()), and the interfaces it implements (getInterfaces()). The Class class, in the java.lang package, has a large number of methods (more than 50). For example, you can test to see if the class is an annotation (isAnnotation()), an interface (isInterface()), or an enumeration (isEnum()). You can see what the object’s fields are (getFields()) or what its methods are (getMethods()), and so on.

hashCode()

The value returned by hashCode() is the object’s hash code, which is the object’s memory address in hexadecimal.

By definition, if two objects are equal, their hash code must also be equal. If you override the equals() method, you change the way two objects are equated and Object’s implementation of hashCode() is no longer valid. Therefore, if you override the equals() method, you must also override the hashCode() method as well.

equals(Object obj)

The equals() method compares two objects for equality and returns true if they are equal. The equals() method provided in the Object class uses the identity operator (==) to determine whether two objects are equal. For primitive data types, this gives the correct result. For objects, however, it does not. The equals() method provided by Object tests whether the object references are equal—that is, if the objects compared are the exact same object. You should always override the equals() method if the identity operator is not appropriate for your class.

clone()

If a class, or one of its superclasses, implements the Cloneable interface, you can use the clone() method to create a copy from an existing object. Object’s implementation of this method checks to see whether the object on which clone() was invoked implements the Cloneable interface. If the object does not, the method throws a CloneNotSupportedException exception. If the object on which clone() was invoked does implement the Cloneable interface, Object’s implementation of the clone() method creates an object of the same class as the original object and initializes the new object’s member variables to have the same values as the original object’s corresponding member variables.

toString()

The Object’s toString() method returns a String representation of the object, which is very useful for debugging. The default toString() method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character - “@”, and the unsigned hexadecimal representation of the hash code of the object. You should always consider overriding the toString() method in your classes.

notify()/notifyAll()

This method is used to wake up all the threads waiting in the waiting queue.

wait()/wait(long timeout)/wait(long timeout,int nanos)

This method is used to put the current thread in the waiting state until any other thread notifies. The time needs to be specified in the function in milliseconds for which you need to resume the thread execution. Note: InterruptedException is thrown by this method.

Links

https://docs.oracle.com/javase/tutorial/java/IandI/objectclass.html
https://www.geeksforgeeks.org/object-class-in-java/
https://www.javatpoint.com/object-class
https://www.educba.com/object-class-in-java/

credit goes to @swayangjit