How Classes are Found

来自 https://docs.oracle.com/javase/8/docs/technotes/tools/findingclasses.html

Java Launcher查找类的顺序

• Bootstrap classes ： java平台自带的类，包括rt.jar(contains all of the compiled class files for the base Java Runtime environment)与其他jre/lib目录下的jar,通过系统属性sun.boot.class.path指定这些bootstrap class的路径
• Extension classes ： Java Extension mechanism的类(The extension mechanism provides a standard, scalable way to make custom APIs available to all applications running on the Java platform),相当于对platform’s core API的扩展，https://docs.oracle.com/javase/tutorial/ext/
• User classes ：　使用　-classpath　参数指定或者在CLASSPATH环境变量中设置

Java Launcher解析JAR中的类

• JAR中的manifest文件描述该jar包的内容