What methods does object class have?

Object class methods include: 1. The clone method that implements shallow copying of objects; 2. The getclass method that obtains the runtime type; 3. The finalize method that releases resources; 4. The hashCode method used for hash search ;5. Make the current thread wait for the lock wait method of the object.

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Object class method

Object is the parent class of all classes, and any class inherits Object by default. What methods does the Object class implement?

(1) Clone method

Protected method to implement shallow copy of the object. This method can only be called if the Cloneable interface is implemented, otherwise a CloneNotSupportedException exception will be thrown.

(2) getClass method

final method to obtain the runtime type.

(3) toString method

This method is commonly used and is generally covered by subclasses.

(4) finalize method

This method is used to release resources. Because it is impossible to determine when this method is called, it is rarely used.

(5) equals method

This method is a very important method. Generally equals and == are different, but in Object they are the same. Subclasses generally override this method.

(6) hashCode method

This method is used for hash search. If you override the equals method, you generally need to rewrite the hashCode method. This method is used in some Collections with hash functions.

Generally must satisfy obj1.equals(obj2)==true. It can be concluded that obj1.hash-Code()==obj2.hashCode(), but equal hashCode does not necessarily satisfy equals. However, in order to improve efficiency, the above two conditions should be made as close to equivalent as possible.

(7) wait method

The wait method is to make the current thread wait for the lock of the object. The current thread must be the owner of the object, that is, it has the object. lock. The wait() method waits until the lock is acquired or interrupted. wait(long timeout) sets a timeout interval and returns if the lock is not obtained within the specified time.

After calling this method, the current thread enters sleep state until the following events occur.

(1) Other threads called the notify method of the object.

(2) Other threads called the notifyAll method of the object.

(3) Other threads call interrupt to interrupt the thread.

(4) The time interval has arrived.

The thread can be scheduled at this time. If it is interrupted, an InterruptedException will be thrown.

(8) notify method

This method wakes up a thread waiting on the object.

(9) notifyAll method

This method wakes up all threads waiting on the object.

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