java源碼Object

1 getClass()方法 ，由注釋可知返回的是運行是實際的類型，不是聲明的類型。

// The Class object that represents the runtime class of this object.

          public final native Class<?> getClass();

2

    /**     * Returns a hash code value for the object. This method is      * supported for the benefit of hashtables such as those provided by      * <code>java.util.Hashtable</code>.      * <p>     * The general contract of <code>hashCode</code> is:      * <ul>     * <li>Whenever it is invoked on the same object more than once during      *     an execution of a Java application, the <tt>hashCode</tt> method      *     must consistently return the same integer, provided no information      *     used in <tt>equals</tt> 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 <tt>equals(Object)</tt>     *     method, then calling the <code>hashCode</code> method on each of      *     the two objects must produce the same integer result.      * <li>It is <em>not</em> required that if two objects are unequal      *     according to the {@link java.lang.Object#equals(java.lang.Object)}      *     method, then calling the <tt>hashCode</tt> 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 hashtables.     * </ul>     * <p>     * As much as is reasonably practical, the hashCode method defined by      * class <tt>Object</tt> does return distinct integers for distinct      * objects. (This is typically implemented by converting the internal      * address of the object into an integer, but this implementation      * technique is not required by the      * Java<font size="-2"><sup>TM</sup></font> programming language.)     *     * @return  a hash code value for this object.     * @see     java.lang.Object#equals(java.lang.Object)     * @see     java.util.Hashtable     */    public native int hashCode();

 

3 equals方法。滿足

        1 自反性

        2 對稱性

        3 傳遞性

        4 一致性（等冪性）

        5 非null的x，調用x.equals(null)，返回false

        6 如果x和y引用同一個對象，（x == y）,當然x.equals(y)返回true。

        7 最重要的是不管equals是否override，都應該override方法，因為需滿足：相等的對象擁有相等的hashCode值。

    Indicates whether some other object is "equal to" this one. The equals method implements an equivalence relation on non-null object references: It is reflexive: for any non-null reference value x, x.equals(x) should return true. It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true. It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true. It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified. For any non-null reference value x, x.equals(null) should return false. The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true). Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.    public boolean equals(Object obj) {return (this == obj);    }

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