Class.forName()详解

官方给出了

 @CallerSensitive
    public static Class forName(String className)
                throws ClassNotFoundException {
        Class caller = Reflection.getCallerClass();
        return forName0(className, true, ClassLoader.getClassLoader(caller), caller);
    }


 @CallerSensitive
    public static Class forName(String name, boolean initialize,
                                   ClassLoader loader)
        throws ClassNotFoundException


//私有方法，是个本地方法，直接调用C JNI  
 /** Called after security check for system loader access checks have been made. */
    private static native Class forName0(String name, boolean initialize,
                                            ClassLoader loader,
                                            Class caller)
        throws ClassNotFoundException;

//测试代码

public class ClassTest {


    public static  void main(String args[]) throws IllegalAccessException, InstantiationException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException {
//        Class clazz1 = A.class;
//
//        System.out.println(clazz1.newInstance().getClass().getSimpleName());
//
//
//        Class clazA = Class.forName("com.wd.bigdata.javaexample.proxy.Class.A");
//                .getConstructor(String.class,int.class,float.class)

        System.out.println("================");

        Class claz = Class.forName("com.wd.bigdata.javaexample.proxy.Class.A",
                false,
                A.class.getClassLoader());

//        Object o = con.newInstance("yang",29,0.2f);
//
//        System.out.println(o.getClass().getName());
//        System.out.println(o.toString());
    }


public class A {

    private String field1;
    private int field2;
    private float field3;


    static {
        System.out.println("A static init");
    }


    public A() {
        System.out.println(" A construct ");
    }

    public A(String field1) {
        this.field1 = field1;
    }

    public A(String field1, int field2) {
        this.field1 = field1;
        this.field2 = field2;
    }

    public A(String field1, int field2, float field3) {
        this.field1 = field1;
        this.field2 = field2;
        this.field3 = field3;
    }
}

第一种通过Class.forName(name) 加载class，对于字节加载到类加载器的过程，主要体现在静态区域的初始化，测试结果也显示，会调用静态快
如果使用第二种方法，将初始参数设置为false，则不会调用静态块，从而可以得出结论，文档中所说的初始化主要是指静态块。
在这两者调用的过程中，都会去调用构造方法，也证明，构造方法主要是实例化对象的时候才会被调用，在Class中从newInstance方法就能体现出来。