听说，你也一直钟爱着equals。。。

脑补一下final

final 用于声明变量/参数/属性、方法和类。

• 修饰变量：如果变量是基本类型，其值不变；如果是对象，则引用不可再变（内容可变）。
• 修饰方法：方法不可重写（是否可继承取决于方法的访问修饰符）
• 修饰类：类不可被继承。

==与equals的区别

我想，大家常规的解释是：==是操作符，比较基本类型，则为其值；比较引用类型，则用以比较两个对象在内存中的哈希地址。 equals是方法，比较的是变量的内容。

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equals是超类Object的方法。参数是一个object对象。本文我将重点借助JAVADOC和源码来阐释。

java.lang.Object里对equals方法的说明：

/**

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.
Parameters:
obj - the reference object with which to compare.
Returns:
true if this object is the same as the obj argument; false otherwise.
See Also:
hashCode(), java.util.HashMap
 */

public boolean equals(Object obj) {

    return (this == obj);
}

可见equals默认是比较对象的哈希值。

String、Integer这些包装类重写了equals方法。重写的逻辑都是先判断类型是否匹配，然后String是看字符串里每个char字符是否都相同，Integer是两个Integer实例的intValue。

//java.lang.String

/**
     * Compares this string to the specified object.  The result is {@code
     * true} if and only if the argument is not {@code null} and is a {@code
     * String} object that represents the same sequence of characters as this
     * object.
*/
    public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String) anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                            return false;
                    i++;
                }
                return true;
            }
        }
        return false;
}



//java.lang.Integer

/**
     * Compares this object to the specified object.  The result is
     * {@code true} if and only if the argument is not
     * {@code null} and is an {@code Integer} object that
     * contains the same {@code int} value as this object.
*/
public boolean equals(Object obj) {
        if (obj instanceof Integer) {
            return value == ((Integer)obj).intValue();
        }
        return false;
}

 比较java枚举成员使用equal还是==》文中分析了分别用==和equals来比较枚举的场景。最终建议是最好用==，也是考虑到了上文中提到的equals的弊端，有效保证了程序的健壮性。 同样，如果是数值比较，也最好用基本类型，因为用==来比较基本类型的数字不存在疑义。