用Class.forName()加载类

class Cls {
    private Cls() {
    }
}

public class ClassTrouble {
    public static void main(String... args) {
        try {
            Class c = Class.forName("Cls");
            c.newInstance(); // InstantiationException

            // production code should handle these exceptions more gracefully
        } catch (InstantiationException x) {
            x.printStackTrace();
        } catch (IllegalAccessException x) {
            x.printStackTrace();
        } catch (ClassNotFoundException x) {
            x.printStackTrace();
        }
    }
}