非也非也, jdk只会加载rt.jar
如果你的程序需要动态调用javac,就把tools.jar加上
C:\>java -verbose
[Opened E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Opened E:\Java\j2sdk1.4.2_02\jre\lib\sunrsasign.jar]
[Opened E:\Java\j2sdk1.4.2_02\jre\lib\jsse.jar]
[Opened E:\Java\j2sdk1.4.2_02\jre\lib\jce.jar]
[Opened E:\Java\j2sdk1.4.2_02\jre\lib\charsets.jar]
[Loaded java.lang.Object from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.io.Serializable from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.lang.Comparable from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.lang.CharSequence from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.lang.String from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.lang.Class from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.lang.Cloneable from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
[Loaded java.lang.ClassLoader from E:\Java\j2sdk1.4.2_02\jre\lib\rt.jar]
...