Myeclipse6.0中没有tools.jar包，所以无法生成 java的class文件
错误如下：
Buildfile: E:\ant\Ant\build.xml
compile:
[mkdir] Created dir: E:\ant\Ant\build\classes
[javac] Compiling 1 source file to E:\ant\Ant\build\classes
BUILD FAILED
E:\ant\Ant\build.xml:7: Error starting modern compiler
Total time: 405 milliseconds
解决办法：去jdk1.5中将tools.jar 拷贝到
MyEclipse 6.0\jre\lib\ext
拷贝前 查看MyEclipse 6.0\jre\lib\ext 里面不存在tools.jar
拷贝后测试则生成class成功