public class 類載入器 {
    public static void main(String[] args) throws IOException {
        //獲取系統類載入器
        ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
        System.out.println(systemClassLoader);
        //獲取拓展類載入器
        ClassLoader extensionClassLoader = systemClassLoader.getParent();
        System.out.println(extensionClassLoader);
        System.out.println(ClassLoader.getPlatformClassLoader());
        //獲取根類載入器,結果無法獲取,為null
        //因為根類載入器沒有繼承ClassLoader抽象類,是C++實現的,所以拓展類載入器的getParent()返回null.
        System.out.println(extensionClassLoader.getParent());

        //獲取系統類載入器的類載入路徑
        Enumeration<URL> enumeration = systemClassLoader.getResources("");
        while (enumeration.hasMoreElements()) {
            System.out.println(enumeration.nextElement());
        }
        //獲取拓展類載入器的類載入路徑
        System.out.println(System.getProperty("java.ext.dirs"));
    }
    
}
 

執行結果如下:

jdk.internal.loader.ClassLoaders$AppClassLoader@2437c6dc
jdk.internal.loader.ClassLoaders$PlatformClassLoader@7c30a502
jdk.internal.loader.ClassLoaders$PlatformClassLoader@7c30a502
null
file:/E:/study/JavaSE/out/production/JavaSE/
null