一.简介：
Java程序中引用变量的类型，分为编译类型和运行类型，编译时类型由声明该变量时使用的类型决定，运行时类型由实际赋给该变量的对象决定。
编译时根本无法预知该对象和类可能属于那些类，程序只依靠运行时信息来发现该对象和类的真实信息，这就用到反射。
二.示例
public interface TestInterface {
}
public class Person implements Serializable,TestInterface{
private Long id;
private String name;
public Person() {
this.id = 100L;
this.name = "name";
}
public Person(Long id, String name) {
this.id = id;
this.name = name;
}
public Person(Long id) {
super();
this.id = id;
}
private Person(String name) {
super();
this.name = name+"private_Person";
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String toString() {
return "Person [id=" + id + ", name=" + name + "]";
}
private String getSomeThing() {
return "getSomeThing";
}
private void testPrivate(){
System.out.println("private testPrivate");
}
}
public class ReflectTest {
public String className=null;
public Class personClass=null;
/**
* 反射Person类
* @throws Exception
*/
@Before
public void init() throws Exception{
className="com.lm.test.java.reflect.Person";
personClass=Class.forName(className);
}
/**
* 获取某个class文件对象
* @throws Exception
*/
@Test
public void getClassName() throws Exception{
System.out.println(personClass);
}
/**
*获取某个class文件对象的另一种方式
*/
@Test
public void getClassName2() throws Exception {
System.out.println(Person.class);
}
/**
* 创建一个class文件表示实例对象，底层会调用空参的构造方法
* @throws Exception
*/
@Test
public void getNewInstance() throws Exception{
System.out.println(personClass.newInstance());
}
/**
* 获取非私有的构造函数
* @throws Exception
*/
@Test
public void getPublicConstructor() throws Exception{
Constructor constructor = personClass.getConstructor(Long.class, String.class);
Person person = (Person) constructor.newInstance(100L, "lisi");
System.out.println(person.getId());
System.out.println(person.getName());
}
/**
* 获取私有的构造函数
* @throws Exception
*/
@Test
public void getPrivateConstructor() throws Exception{
Constructor declaredConstructor = personClass.getDeclaredConstructor(String.class);
declaredConstructor.setAccessible(true); //强制取消Java权限检查
Person person = (Person) declaredConstructor.newInstance("lisi2");
System.out.println(person.getName()+" getPrivateConstructor");
}
/**
* 获取非私有成员函数
* @throws Exception
*/
@Test
public void getNotPrivateField() throws Exception{
Constructor constructor = personClass.getConstructor(Long.class, String.class);
Object object = personClass.newInstance();
Method toStringMethod = personClass.getMethod("toString");
Object object2 = toStringMethod.invoke(object);
System.out.println(object2);
}
/**
*获取私有的成员函数
*/
@SuppressWarnings("unchecked")
@Test
public void getPrivateMethod() throws Exception {
Object obj = personClass.newInstance();//获取空参的构造函数
Method method = personClass.getDeclaredMethod("getSomeThing");
method.setAccessible(true);
Object value = method.invoke(obj);
System.out.println(value);
}
/**
*
*/
@Test
public void otherMethod() throws Exception {
//当前加载这个class文件的那个类加载器对象
System.out.println(personClass.getClassLoader());
//获取某个类实现的所有接口
Class[] interfaces = personClass.getInterfaces();
for (Class class1 : interfaces) {
System.out.println(class1);
}
//反射当前这个类的直接父类
System.out.println(personClass.getGenericSuperclass());
//判断当前的Class对象表示是否是数组
System.out.println(personClass.isArray());
System.out.println(new String[3].getClass().isArray());
}
}