最近看了网上有人说，String对象的equals()与==的区别，不知道两者到底有什么区别，如果真的要彻底搞清楚，我们还是从“万类之源”说起，http://blog.itpub.net/29876893/viewspace-1819489/这是之前写关于Object的一篇文章，现在我们还是从源码入手（当然结合API更好）。
下面还是分析Object类中的equals()方法，关于源码如何获取上篇文章已经说的很清楚。

下面是Object类中的equals（）：

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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:
*
*
```
			
```
* x.clone() != x
* will be true, and that the expression:
*
*
```
			
```
* x.clone().getClass() == x.getClass()
* will be {@code true}, but these are not absolute requirements.
* While it is typically the case that:
*
*
```
			
```
* x.clone().equals(x)
* 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.
* @exception 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
*/

从上面我们可以看出来，比较的是两个对象的地址值，更全面的介绍，自己看下上面的注释。

下面看下toString()方法，当然和本篇没有多少关系。

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public String toString() {
return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

返回的是包名.类名@十六进制的哈希值

下面看一小程序：

上面结果也许你会问，不都是字符串么！为什么结果不一样呢！？这个要结合java内存来分析，对于new出来的对象，是在堆中分配内存空间，而对于String类很特殊，
如果对于直接String ss = xxxx,是在常量池中分配内存空间，并不是在栈中分配。但是对于上述的a,b在栈中分配空间，指向了堆中不同的内存空间，当然两者不等！

再看一个小程序：

咦，equals（）不是比较的是地址么？还是true，不能有这种定向思维，应该查阅API或者看下源码：

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*/
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;
}

上面很清楚，String类重写了Object中的toString()方法，如果不是指向同一对象的话，那就比较内容是不是一样，所以上文中a.equals(b),b.equals(a)返回的是true.
在继承父类时，重写某个方法很重要。上文中没有说Object类中一个也很重要的方法hashcode(),这也是后续文章会写。文章作为本人学习总结，如有错误之处，请指正！谢谢。

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String对象的equals（）与 = =

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