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关于类加载的双亲委派机制的测试

作者:互联网

0.背景

最近又想到了双亲委派机制,然后决定做一个小实验来验证下理论。

于是有了接下来的测试。

 

1.测试

测试1:

创建一个User.java类,放在D:\\jc文件夹下

用 javac编译生成User.class文件

创建测试类Test

public class Test {

    public static void main(String[] args) throws Exception{
        File file = new File("D:\\jc");
        URL url = file.toURI().toURL();
        ClassLoader loader1 = new URLClassLoader(new URL[]{url});
        Class<?> clazz1 = loader1.loadClass("User");
        System.out.println("当前类加载器" + clazz1.getClassLoader());
        System.out.println("父类加载器" + clazz1.getClassLoader().getParent());

        ClassLoader loader2 = new URLClassLoader(new URL[]{url});
        Class<?> clazz2 = loader2.loadClass("User");
        System.out.println("当前类加载器" + clazz2.getClassLoader());
        System.out.println("父类加载器" + clazz2.getClassLoader().getParent());

        System.out.println(clazz1 == clazz2);

    }
}

输出  

当前类加载器java.net.URLClassLoader@4b85612c
父类加载器sun.misc.Launcher$AppClassLoader@18b4aac2
当前类加载器java.net.URLClassLoader@5c29bfd
父类加载器sun.misc.Launcher$AppClassLoader@18b4aac2
false

 

测试2:

创建一个User.java类,放在D:\\jc文件夹下

用 javac编译生成User.class文件

创建测试类Test

public class Test {

    public static void main(String[] args) throws Exception{
        File file = new File("D:\\jc");
        URL url = file.toURI().toURL();
        ClassLoader loader1 = new URLClassLoader(new URL[]{url});
        Class<?> clazz1 = loader1.loadClass("User");
        System.out.println("当前类加载器" + clazz1.getClassLoader());
        System.out.println("父类加载器" + clazz1.getClassLoader().getParent());

        //ClassLoader loader2 = new URLClassLoader(new URL[]{url});
        Class<?> clazz2 = loader1.loadClass("User");
        System.out.println("当前类加载器" + clazz2.getClassLoader());
        System.out.println("父类加载器" + clazz2.getClassLoader().getParent());

        System.out.println(clazz1 == clazz2);

    }
}

输出

当前类加载器java.net.URLClassLoader@4b85612c
父类加载器sun.misc.Launcher$AppClassLoader@18b4aac2
当前类加载器java.net.URLClassLoader@4b85612c
父类加载器sun.misc.Launcher$AppClassLoader@18b4aac2
true

 

测试3:

在当前测试类Test的pakage下创建一个User.java(相当于在classpath下加载User类)

public class Test {

    public static void main(String[] args) throws Exception{
        File file = new File("./");
        URL url = file.toURI().toURL();
        ClassLoader loader1 = new URLClassLoader(new URL[]{url});
        Class<?> clazz1 = loader1.loadClass("com.ouym.test.User");
        System.out.println("当前类加载器" + clazz1.getClassLoader());
        System.out.println("父类加载器" + clazz1.getClassLoader().getParent());

        ClassLoader loader2 = new URLClassLoader(new URL[]{url});
        Class<?> clazz2 = loader2.loadClass("com.ouym.test.User");
        System.out.println("当前类加载器" + clazz2.getClassLoader());
        System.out.println("父类加载器" + clazz2.getClassLoader().getParent());

        System.out.println(clazz1 == clazz2);

    }
}

输出

当前类加载器sun.misc.Launcher$AppClassLoader@18b4aac2
父类加载器sun.misc.Launcher$ExtClassLoader@4b85612c
当前类加载器sun.misc.Launcher$AppClassLoader@18b4aac2
父类加载器sun.misc.Launcher$ExtClassLoader@4b85612c
true

 

2.实验总结

这是一次双亲委派模型的实验

对比实验1和实验2发现了什么?

对比实验1和实验3又发现了什么?

 

标签:委派,System,双亲,User,println,new,out,加载
来源: https://www.cnblogs.com/ouym/p/16578045.html