manual

Java 8. Manual Loading

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Task: load any application class using a custom class loader (CustomClassLoader).

Solution

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Project with three classes:

• Main - a class containing the main method, where an instance of the CustomClassLoader class is created, the Cat class is loaded using it, creating an instance of the class Cat and calling the Cat::talk method;
• Cat - loadable class with the talk method, which prints the string "Meow" to stdout;
• CustomClassLoader - a class that is an implementation of a custom class loader.

Run

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java8 -cp . ru.ispras.j8.manual.Main

or

java8 -jar manual-1.0.jar

Output:

System ClassLoader is ru.ispras.j8.manual.CustomClassLoader@75b84c92
Main Class ClassLoader is ru.ispras.j8.manual.CustomClassLoader@75b84c92
Cat Class ClassLoader is ru.ispras.j8.manual.CustomClassLoader@75b84c92
Meow

Explanation

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• When a CustomClassLoader is created, its parent becomes sun.misc.Launcher$AppClassLoader.

Notes

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• CustomClassLoader gets some system classes to be loaded first, for example classes from java.* packages. If you try to load a class from the java.* package, the JVM will throw java.lang.SecurityException: Prohibited package name: java.*.