JDK中String类的实现不再是以往的（copy-on-write + 共享字符数组）了，而是每个字符串对象都有自己的字符数组

StringReflection.java

package problem.java.lang.reflect;

import java.lang.reflect.Field;

public class StringReflection {

    /**
     * $ java -version
     * java version "1.7.0_45"
     * Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
     * Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)
     */

    public static void main(String[] args) throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
        String s1 = "Hello World";  
        String s2 = "Hello World";  
        String s3 = s1.substring(6);  
        System.out.println(s1); // Hello World  
        System.out.println(s2); // Hello World  
        System.out.println(s3); // World  

        Field field = String.class.getDeclaredField("value");  
        field.setAccessible(true);  
        char[] value = (char[])field.get(s1);  
        value[6] = 'J';  
        value[7] = 'a';  
        value[8] = 'v';  
        value[9] = 'a';  
        value[10] = '!';  

        System.out.println(s1); // Hello Java!  
        System.out.println(s2); // Hello Java!  
        System.out.println(s3); // World  
    }

}