面向对象进阶篇2-object类源码

这个类里面的方法都可以直接拿过来用，因为所有java类都继承了这个类

如任一选择一个class，ctrl + T / command + T

，

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package java.lang;

import jdk.internal.vm.annotation.IntrinsicCandidate;

/**

* Class {@code Object} is the root of the class hierarchy.

* Every class has {@code Object} as a superclass. All objects,

* including arrays, implement the methods of this class.

* @see java.lang.Class

* @since 1.0

public class Object {

/**

* Constructs a new object.

@IntrinsicCandidate

public Object() {}

/**

* Returns the runtime class of this {@code Object}. The returned

* {@code Class} object is the object that is locked by {@code

* static synchronized} methods of the represented class.

* The actual result type is {@code Class<? extends |X|>}

* where {@code |X|} is the erasure of the static type of the

* expression on which {@code getClass} is called. For

* example, no cast is required in this code fragment:

*

* {@code Number n = 0; }

* {@code Class<? extends Number> c = n.getClass(); }

*

* @return The {@code Class} object that represents the runtime

* class of this object.

* @jls 15.8.2 Class Literals

@IntrinsicCandidate

public final native Class<?> getClass();

/**

* Returns a hash code value for the object. This method is

* supported for the benefit of hash tables such as those provided by

* {@link java.util.HashMap}.

*

* The general contract of {@code hashCode} is:

* <ul>

* <li>Whenever it is invoked on the same object more than once during

* an execution of a Java application, the {@code hashCode} method

* must consistently return the same integer, provided no information

* used in {@code equals} comparisons on the object is modified.

* This integer need not remain consistent from one execution of an

* application to another execution of the same application.

* <li>If two objects are equal according to the {@code equals(Object)}

* method, then calling the {@code hashCode} method on each of

* the two objects must produce the same integer result.

* <li>It is not required that if two objects are unequal

* according to the {@link java.lang.Object#equals(java.lang.Object)}

* method, then calling the {@code hashCode} method on each of the

* two objects must produce distinct integer results. However, the

* programmer should be aware that producing distinct integer results

* for unequal objects may improve the performance of hash tables.

* </ul>

* @implSpec

* As far as is reasonably practical, the {@code hashCode} method defined

* by class {@code Object} returns distinct integers for distinct objects.

* @return a hash code value for this object.

* @see java.lang.Object#equals(java.lang.Object)

* @see java.lang.System#identityHashCode

@IntrinsicCandidate

public native int hashCode();

/**

* Indicates whether some other object is "equal to" this one.

*

* The {@code equals} method implements an equivalence relation

* on non-null object references:

* <ul>

* <li>It is reflexive: for any non-null reference value

* {@code x}, {@code x.equals(x)} should return

* {@code true}.

* <li>It is symmetric: for any non-null reference values

* {@code x} and {@code y}, {@code x.equals(y)}

* should return {@code true} if and only if

* {@code y.equals(x)} returns {@code true}.

* <li>It is transitive: for any non-null reference values

* {@code x}, {@code y}, and {@code z}, if

* {@code x.equals(y)} returns {@code true} and

* {@code y.equals(z)} returns {@code true}, then

* {@code x.equals(z)} should return {@code true}.

* <li>It is consistent: for any non-null reference values

* {@code x} and {@code y}, multiple invocations of

* {@code x.equals(y)} consistently return {@code true}

* or consistently return {@code false}, provided no

* information used in {@code equals} comparisons on the

* objects is modified.

* <li>For any non-null reference value {@code x},

* {@code x.equals(null)} should return {@code false}.

* </ul>

*

* The {@code equals} method for class {@code Object} implements

* the most discriminating possible equivalence relation on objects;

* that is, for any non-null reference values {@code x} and

* {@code y}, this method returns {@code true} if and only

* if {@code x} and {@code y} refer to the same object

* ({@code x == y} has the value {@code true}).

*

* Note that it is generally necessary to override the {@code hashCode}

* method whenever this method is overridden, so as to maintain the

* general contract for the {@code hashCode} method, which states

* that equal objects must have equal hash codes.

* @param obj the reference object with which to compare.

* @return {@code true} if this object is the same as the obj

* argument; {@code false} otherwise.

* @see #hashCode()

* @see java.util.HashMap

public boolean equals(Object obj) {

return (this == obj);

}

/**

* Creates and returns a copy of this object. The precise meaning

* of "copy" may depend on the class of the object. The general

* intent is that, for any object {@code x}, the expression:

* <blockquote>

* <pre>

* x.clone() != x</pre></blockquote>

* will be true, and that the expression:

* <blockquote>

* <pre>

* x.clone().getClass() == x.getClass()</pre></blockquote>

* will be {@code true}, but these are not absolute requirements.

* While it is typically the case that:

* <blockquote>

* <pre>

* x.clone().equals(x)</pre></blockquote>

* will be {@code true}, this is not an absolute requirement.

*

* By convention, the returned object should be obtained by calling

* {@code super.clone}. If a class and all of its superclasses (except

* {@code Object}) obey this convention, it will be the case that

* {@code x.clone().getClass() == x.getClass()}.

*

* By convention, the object returned by this method should be independent

* of this object (which is being cloned). To achieve this independence,

* it may be necessary to modify one or more fields of the object returned

* by {@code super.clone} before returning it. Typically, this means

* copying any mutable objects that comprise the internal "deep structure"

* of the object being cloned and replacing the references to these

* objects with references to the copies. If a class contains only

* primitive fields or references to immutable objects, then it is usually

* the case that no fields in the object returned by {@code super.clone}

* need to be modified.

*

* The method {@code clone} for class {@code Object} performs a

* specific cloning operation. First, if the class of this object does

* not implement the interface {@code Cloneable}, then a

* {@code CloneNotSupportedException} is thrown. Note that all arrays

* are considered to implement the interface {@code Cloneable} and that

* the return type of the {@code clone} method of an array type {@code T[]}

* is {@code T[]} where T is any reference or primitive type.

* Otherwise, this method creates a new instance of the class of this

* object and initializes all its fields with exactly the contents of

* the corresponding fields of this object, as if by assignment; the

* contents of the fields are not themselves cloned. Thus, this method

* performs a "shallow copy" of this object, not a "deep copy" operation.

*

* The class {@code Object} does not itself implement the interface

* {@code Cloneable}, so calling the {@code clone} method on an object

* whose class is {@code Object} will result in throwing an

* exception at run time.

* @return a clone of this instance.

* @throws CloneNotSupportedException if the object's class does not

* support the {@code Cloneable} interface. Subclasses

* that override the {@code clone} method can also

* throw this exception to indicate that an instance cannot

* be cloned.

* @see java.lang.Cloneable

@IntrinsicCandidate

protected native Object clone() throws CloneNotSupportedException;

/**

* Returns a string representation of the object. In general, the

* {@code 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.

*

* The {@code toString} method for class {@code Object}

* returns a string consisting of the name of the class of which the

* object is an instance, the at-sign character `{@code @}', and

* the unsigned hexadecimal representation of the hash code of the

* object. In other words, this method returns a string equal to the

* value of:

* <blockquote>

* <pre>

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

* </pre></blockquote>

* @return a string representation of the object.

public String toString() {

return getClass().getName() + "@" + Integer.toHexString(hashCode());

}

/**

* 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. The choice is arbitrary and occurs at

* the discretion of the implementation. A thread waits on an object's

* monitor by calling one of the {@code wait} methods.

*

* The awakened thread will not be able to proceed until the current

* thread relinquishes the lock on this object. The awakened thread will

* compete in the usual manner with any other threads that might be

* actively competing to synchronize on this object; for example, the

* awakened thread enjoys no reliable privilege or disadvantage in being

* the next thread to lock this object.

*

* This method should only be called by a thread that is the owner

* of this object's monitor. A thread becomes the owner of the

* object's monitor in one of three ways:

* <ul>

* <li>By executing a synchronized instance method of that object.

* <li>By executing the body of a {@code synchronized} statement

* that synchronizes on the object.

* <li>For objects of type {@code Class,} by executing a

* synchronized static method of that class.

* </ul>

*

* Only one thread at a time can own an object's monitor.

* @throws IllegalMonitorStateException if the current thread is not

* the owner of this object's monitor.

* @see java.lang.Object#notifyAll()

* @see java.lang.Object#wait()

@IntrinsicCandidate

public final native void notify();

/**

* 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

* {@code wait} methods.

*

* The awakened threads will not be able to proceed until the current

* thread relinquishes the lock on this object. The awakened threads

* will compete in the usual manner with any other threads that might

* be actively competing to synchronize on this object; for example,

* the awakened threads enjoy no reliable privilege or disadvantage in

* being the next thread to lock this object.

*

* This method should only be called by a thread that is the owner

* of this object's monitor. See the {@code notify} method for a

* description of the ways in which a thread can become the owner of

* a monitor.

* @throws IllegalMonitorStateException if the current thread is not

* the owner of this object's monitor.

* @see java.lang.Object#notify()

* @see java.lang.Object#wait()

@IntrinsicCandidate

public final native void notifyAll();

/**

* Causes the current thread to wait until it is awakened, typically

* by being notified or interrupted.

*

* In all respects, this method behaves as if {@code wait(0L, 0)}

* had been called. See the specification of the {@link #wait(long, int)} method

* for details.

* @throws IllegalMonitorStateException if the current thread is not

* the owner of the object's monitor

* @throws InterruptedException if any thread interrupted the current thread before or

* while the current thread was waiting. The interrupted status of the

* current thread is cleared when this exception is thrown.

* @see #notify()

* @see #notifyAll()

* @see #wait(long)

* @see #wait(long, int)

public final void wait() throws InterruptedException {

wait(0L);

}

/**

* Causes the current thread to wait until it is awakened, typically

* by being notified or interrupted, or until a

* certain amount of real time has elapsed.

*

* In all respects, this method behaves as if {@code wait(timeoutMillis, 0)}

* had been called. See the specification of the {@link #wait(long, int)} method

* for details.

* @param timeoutMillis the maximum time to wait, in milliseconds

* @throws IllegalArgumentException if {@code timeoutMillis} is negative

* @throws IllegalMonitorStateException if the current thread is not

* the owner of the object's monitor

* @throws InterruptedException if any thread interrupted the current thread before or

* while the current thread was waiting. The interrupted status of the

* current thread is cleared when this exception is thrown.

* @see #notify()

* @see #notifyAll()

* @see #wait()

* @see #wait(long, int)

public final native void wait(long timeoutMillis) throws InterruptedException;

/**

* Causes the current thread to wait until it is awakened, typically

* by being notified or interrupted, or until a

* certain amount of real time has elapsed.

*

* The current thread must own this object's monitor lock. See the

* {@link #notify notify} method for a description of the ways in which

* a thread can become the owner of a monitor lock.

*

* This method causes the current thread (referred to here as <var>T</var>) to

* place itself in the wait set for this object and then to relinquish any

* and all synchronization claims on this object. Note that only the locks

* on this object are relinquished; any other objects on which the current

* thread may be synchronized remain locked while the thread waits.

*

* Thread <var>T</var> then becomes disabled for thread scheduling purposes

* and lies dormant until one of the following occurs:

* <ul>

* <li>Some other thread invokes the {@code notify} method for this

* object and thread <var>T</var> happens to be arbitrarily chosen as

* the thread to be awakened.

* <li>Some other thread invokes the {@code notifyAll} method for this

* object.

* <li>Some other thread {@linkplain Thread#interrupt() interrupts}

* thread <var>T</var>.

* <li>The specified amount of real time has elapsed, more or less.

* The amount of real time, in nanoseconds, is given by the expression

* {@code 1000000 * timeoutMillis + nanos}. If {@code timeoutMillis} and {@code nanos}

* are both zero, then real time is not taken into consideration and the

* thread waits until awakened by one of the other causes.

* <li>Thread <var>T</var> is awakened spuriously. (See below.)

* </ul>

*

* The thread <var>T</var> is then removed from the wait set for this

* object and re-enabled for thread scheduling. It competes in the

* usual manner with other threads for the right to synchronize on the

* object; once it has regained control of the object, all its

* synchronization claims on the object are restored to the status quo

* ante - that is, to the situation as of the time that the {@code wait}

* method was invoked. Thread <var>T</var> then returns from the

* invocation of the {@code wait} method. Thus, on return from the

* {@code wait} method, the synchronization state of the object and of

* thread {@code T} is exactly as it was when the {@code wait} method

* was invoked.

*

* A thread can wake up without being notified, interrupted, or timing out, a

* so-called spurious wakeup. While this will rarely occur in practice,

* applications must guard against it by testing for the condition that should

* have caused the thread to be awakened, and continuing to wait if the condition

* is not satisfied. See the example below.

*

* For more information on this topic, see section 14.2,

* "Condition Queues," in Brian Goetz and others' Java Concurrency

* in Practice (Addison-Wesley, 2006) or Item 69 in Joshua

* Bloch's Effective Java, Second Edition (Addison-Wesley,

* 2008).

*

* If the current thread is {@linkplain java.lang.Thread#interrupt() interrupted}

* by any thread before or while it is waiting, then an {@code InterruptedException}

* is thrown. The interrupted status of the current thread is cleared when

* this exception is thrown. This exception is not thrown until the lock status of

* this object has been restored as described above.

* @apiNote

* The recommended approach to waiting is to check the condition being awaited in

* a {@code while} loop around the call to {@code wait}, as shown in the example

* below. Among other things, this approach avoids problems that can be caused

* by spurious wakeups.

* <pre>{@code

* synchronized (obj) {

* while (<condition does not hold> and <timeout not exceeded>) {

* long timeoutMillis = ... ; // recompute timeout values

* int nanos = ... ;

* obj.wait(timeoutMillis, nanos);

* }

* ... // Perform action appropriate to condition or timeout

* }

* }</pre>

* @param timeoutMillis the maximum time to wait, in milliseconds

* @param nanos additional time, in nanoseconds, in the range 0-999999 inclusive

* @throws IllegalArgumentException if {@code timeoutMillis} is negative,

* or if the value of {@code nanos} is out of range

* @throws IllegalMonitorStateException if the current thread is not

* the owner of the object's monitor

* @throws InterruptedException if any thread interrupted the current thread before or

* while the current thread was waiting. The interrupted status of the

* current thread is cleared when this exception is thrown.

* @see #notify()

* @see #notifyAll()

* @see #wait()

* @see #wait(long)

public final void wait(long timeoutMillis, int nanos) throws InterruptedException {

if (timeoutMillis < 0) {

throw new IllegalArgumentException("timeoutMillis value is negative");

}

if (nanos < 0 || nanos > 999999) {

throw new IllegalArgumentException(

"nanosecond timeout value out of range");

}

if (nanos > 0 && timeoutMillis < Long.MAX_VALUE) {

timeoutMillis++;

}

wait(timeoutMillis);

}

/**

* 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 {@code finalize} method to dispose of

* system resources or to perform other cleanup.

*

* The general contract of {@code finalize} is that it is invoked

* if and when the Java virtual

* machine has determined that there is no longer any

* means by which this object can be accessed by any thread that has

* not yet died, except as a result of an action taken by the

* finalization of some other object or class which is ready to be

* finalized. The {@code finalize} method may take any action, including

* making this object available again to other threads; the usual purpose

* of {@code finalize}, however, is to perform cleanup actions before

* the object is irrevocably discarded. For example, the finalize method

* for an object that represents an input/output connection might perform

* explicit I/O transactions to break the connection before the object is

* permanently discarded.

*

* The {@code finalize} method of class {@code Object} performs no

* special action; it simply returns normally. Subclasses of

* {@code Object} may override this definition.

*

* The Java programming language does not guarantee which thread will

* invoke the {@code finalize} method for any given object. It is

* guaranteed, however, that the thread that invokes finalize will not

* be holding any user-visible synchronization locks when finalize is

* invoked. If an uncaught exception is thrown by the finalize method,

* the exception is ignored and finalization of that object terminates.

*

* After the {@code finalize} method has been invoked for an object, no

* further action is taken until the Java virtual machine has again

* determined that there is no longer any means by which this object can

* be accessed by any thread that has not yet died, including possible

* actions by other objects or classes which are ready to be finalized,

* at which point the object may be discarded.

*

* The {@code finalize} method is never invoked more than once by a Java

* virtual machine for any given object.

*

* Any exception thrown by the {@code finalize} method causes

* the finalization of this object to be halted, but is otherwise

* ignored.

* @apiNote

* Classes that embed non-heap resources have many options

* for cleanup of those resources. The class must ensure that the

* lifetime of each instance is longer than that of any resource it embeds.

* {@link java.lang.ref.Reference#reachabilityFence} can be used to ensure that

* objects remain reachable while resources embedded in the object are in use.

*

* A subclass should avoid overriding the {@code finalize} method

* unless the subclass embeds non-heap resources that must be cleaned up

* before the instance is collected.

* Finalizer invocations are not automatically chained, unlike constructors.

* If a subclass overrides {@code finalize} it must invoke the superclass

* finalizer explicitly.

* To guard against exceptions prematurely terminating the finalize chain,

* the subclass should use a {@code try-finally} block to ensure

* {@code super.finalize()} is always invoked. For example,

* <pre>{@code @Override

* protected void finalize() throws Throwable {

* try {

* ... // cleanup subclass state

* } finally {

* super.finalize();

* }

* }</pre>

* @deprecated The finalization mechanism is inherently problematic.

* Finalization can lead to performance issues, deadlocks, and hangs.

* Errors in finalizers can lead to resource leaks; there is no way to cancel

* finalization if it is no longer necessary; and no ordering is specified

* among calls to {@code finalize} methods of different objects.

* Furthermore, there are no guarantees regarding the timing of finalization.

* The {@code finalize} method might be called on a finalizable object

* only after an indefinite delay, if at all.

* Classes whose instances hold non-heap resources should provide a method

* to enable explicit release of those resources, and they should also

* implement {@link AutoCloseable} if appropriate.

* The {@link java.lang.ref.Cleaner} and {@link java.lang.ref.PhantomReference}

* provide more flexible and efficient ways to release resources when an object

* becomes unreachable.

* @throws Throwable the {@code Exception} raised by this method

* @see java.lang.ref.WeakReference

* @see java.lang.ref.PhantomReference

* @jls 12.6 Finalization of Class Instances

@Deprecated(since="9")

protected void finalize() throws Throwable { }

}

面向对象进阶篇2-object类源码

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