The class path is a place in memory where your class files and other resources (* .properties, * .xml, among many other types of resources) become available to programs running in the JVM.
The Eclipse build path is just a folder in which Eclipse will place the result of any build process: this process usually involves compiling the classes, but it can also include other steps, such as generating the code, depending on the -ins plug-in, which can be installed.
Since you can run your program from Eclipse, the build path and class path may contain the same resources. However, keep in mind that the "build path" is a representation of your resources in terms of the operating system's file system, and Classpath is a representation of your resources in terms of the Java virtual machine.
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