tomcat automatically compile the java can not use

I am using JDK1.5 tomcat5.5 import an original project that can be used to start operating normally, after the modified java file 500 error , thought it was an incorrect statement , looking for a good no cause .
then modify a java file , it will automatically re- compile , and then change back to the original statement, the new translation of the java files can not
then used in the cmd "javac java file . java" compiled class files and then copied back to tomcat in WEB-INF \ classes directory can be normal operation. Description tomcat automatically compiles a problem
can only be used in cmd javac compiler can not compile with java ,
please help look for what is the reason ? How to solve ?
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you modify the java files in myeclipse , myeclipse automatically compiled and deployed to the tomcat . It is possible that not configured the tomcat myeclipse jdk, or yes. . . . . .
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is compiled class files .
modified java files should only be restarted after the time will compile it.
compiled class files imperative javac
java class file is executed the commands it
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tomcat has compiled functionality ?
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Your TOMCAT really strong , as well as compilation .
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is my tomcat do not understand . I see the modified java files in the project directory WebRoot \ WEB-INF \ classes in the same name as the class file will automatically change the modification date. Is not calling jdk tomcat java files compiled ? But not able to compile the file , their own state in cmd DOS compiled with javac and then copied to WebRoot \ WEB-INF \ classes directory instead of the original class files ( manually compiled smaller than the automatic translation ) can normal use , but it would be too inconvenient.

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thank bill0605030109 indeed myeclipse in the Java compiler options is not correct, the JKD consistency compiler conformance levels can be selected as 5.0 , turned out to be 6.0 , thanks