Object:

Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class.

是所有类的超类。

1.getClass()：

Returns the runtime class of this Object. The returned Class object is the object that is locked by static synchronized methods of the represented class.

2.hashCode()：

Returns a hash code value for the object.

3.equals(Object obj)：

4.clone()：

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Creates and returns a copy of this object. The precise meaning of "copy" may depend on the class of the object.

意思是：准确的说克隆的意思是，得到类的class和原来类的class是一样的，如下：

public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();
        //false
        System.out.println(arrayList == arrayList.clone());
        //true
        System.out.println(arrayList.getClass() == arrayList.clone().getClass());
        //true
        System.out.println(arrayList.clone().equals(arrayList));
    }

5.toString()：
Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.
推荐所有子类重写这个方法。
默认返回：getClass().getName() + "@" + Integer.toHexString(hashCode());

public static void main(String[] args) {
        Object o = new Object();
        //java.lang.Object@4554617c
        System.out.println(o.toString());
    }

6.notify()：

Wakes up a single thread that is waiting on this object's monitor. If any threads are waiting on this object, one of them is chosen to be awakened.

7.notifyAll()：

Wakes up all threads that are waiting on this object's monitor. A thread waits on an object's monitor by calling one of the wait methods.

8.wait()、wait(long timeout)：

Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed.

9.finalize()：

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

意思是当GC确定这个对象没有任何引用时候，由gc调用这个方法。子类重写finalize（）方法来中断系统资源或者做清理。

JDK8源码阅读笔记--------java.lang.Object

Object:

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