常量池的说明：
常量池之前是放在方法区里面的，也就是在永久代里面的，从JDK7开始移到了堆里面。这一改变我们可以从oracle的release version的notes里的** Important RFEs Addressed in JDK 7 **看到。
Area:HotSpot
Synopsis:
In JDK 7, interned strings are no longer allocated in the permanent generation of the Java heap, but are instead allocated in the main part of the Java heap (known as the young and old generations), along with the other objects created by the application. This change will result in more data residing in the main Java heap, and less data in the permanent generation, and thus may require heap sizes to be adjusted. Most applications will see only relatively small differences in heap usage due to this change, but larger applications that load many classes or make heavy use of the String.intern() method will see more significant differences.
RFE: 6962931
String内存位置说明：
1、显式的String常量
String a = "holten";
String b = "holten";
- 第一句代码执行后就在常量池中创建了一个值为holten的String对象；
- 第二句执行时，因为常量池中存在holten所以就不再创建新的String对象了。
- 此时该字符串的引用在虚拟机栈里面。
2、 String对象
String a = new String("holtenObj");
String b = new String("holtenObj");
- Class被加载时就在常量池中创建了一个值为holtenObj的String对象，第一句执行时会在堆里创建new String(“holtenObj”)对象；
- 第二句执行时，因为常量池中存在holtenObj所以就不再创建新的String对象了，直接在堆里创建new String(“holtenObj”)对象
验证一下:
/**
* Created by holten.gao on 2016/8/16.
*/
public class Main {
public static void main(String[] args){
String str1 = "高小天";
String str2 = "高小天";
System.out.println(str1==str2);//true
String str3 = new String("高大天");
String str4 = new String("高大天");
System.out.println(str3==str4);//false
}
返回结果：
true
false
