Java source code reading of Java lang.Object

Object is the parent class of all classes. Any class inherits object by default. What methods does the object class implement?

1. Clone method

Protect the method and realize the shallow replication of objects. This method can be called only when the clonable interface is implemented. Otherwise, a clonnotsupportedexception exception will be thrown.

2. GetClass method

Final method to get the runtime type.

3. ToString method

This method is used more, and generally subclasses have coverage.

4. Finalize method

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

5. Equals method

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

6. Hashcode method

This method is used for hash lookup. The equals method is rewritten. Generally, the hashcode method is rewritten. This method is used in some collections with hash function.

Generally, obj 1 must be met equals(obj2)==true。 Can launch obj 1 hash-Code()==obj2. Hashcode(), but equal hashcodes do not necessarily satisfy equals. However, in order to improve efficiency, we should try to make the above two conditions close to equivalence.

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 lock of the object. The wait () method waits until it obtains a lock or is interrupted. Wait (longtimeout) sets a timeout interval. If the lock is not obtained within the specified time, it returns.

After calling this method, the current thread goes to sleep until the following events occur.

(1) Another thread called the notify method of the object.

(2) The notifyAll method of the object was called by another thread.

(3) Another thread called interrupt to interrupt the thread.

(4) The time interval is up.

At this point, the thread can be scheduled. If it is interrupted, an interruptedexception exception 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.

―Object―

ClassObjectistherootoftheclasshierarchy. EveryclasshasObjectasasuperclass. Allobjects,includingarrays,implementthemethodsofthisclass.―― FromOracle

― interpretation ―

The object class is the parent class inherited by all objects in Java. Even the array inherits this parent class (it can be understood as the original class, the ancestor of all classes. You may want to ask: is the first class written by James object?).

The inheritance of all classes to the object class is implicit, so it cannot be seen.

―Object―

Default construction method

―clone―

―equals―

Indicateswhethersomeotherobjectis"equalto"thisone.

Theequalsmethodimplementsanequivalencerelationonnon-nullobjectreferences:―FromORacle―

The equals of the original class object compares the references of non empty objects of two variables.

Source code:

Through the source code, we can see that the original class equals is actually equivalent to "= =".

―finalize―

―getClass―

―hashcode―

IntheJavaprogramminglanguage,everyclassimplicitlyorexplicitlyprovidesahashCode()method,whichdigeststhedatastoredinaninstanceoftheclassintoasinglehashvalue(a32-bitsignedinteger). ThishashisusedbyothercodewhenstoringormanipulatingtheinstanceCthevaluesareintendedtobeevenlydistributedforvariedinputsforuseinclustering. Thispropertyisimportanttotheperformanceofhashtablesandotherdatastructuresthatstoreobjectsingroups("buckets")basedontheircomputedhashvalues. Technically,inJava,hashCode()bydefaultisanativemethod,meaning,ithasthemodifier'native',asitisimplementeddirectlyinthenativecodeintheJVM.

Source：Wikipedia

Each class in Java implicitly or explicitly implements the hashcode method of object.

To sum up with Google and official individuals, why should the author have hashcode in the original class?

① Storage optimization of class objects to facilitate the search of class objects.

② Use with equals.

Note: many blogs say that the hashcode method returns the physical storage address or logical storage address of the class. This statement is wrong. According to the official statement, the returned 32-bit value is only related to the storage location of the class object.

―notify―

―notifyall―

―toString―

ThetoStringmethodforclassObjectreturnsastringconsistingofthenameoftheclassofwhichtheobjectisaninstance,theat-signcharacter`@',andtheunsignedhexadecimalrepresentationofthehashcodeoftheobject. Inotherwords,thismethodreturnsastringequaltothevalueof:

getClass(). getName()+'@'+Integer. toHexString(hashCode())

Source code:

Returns a hash value in the form of class name + @ + of the class.

―wait―

finalize()

summary

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