【Java面试指北】反射(1) 初识反射 - ToB企服应用市场:ToB评测及商务社交产业平台

Student student = new Student();

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// 这里的“com.demo.Student”是需要反射的类的全限定名（包名+类名）
Class clz = Class.forName("com.demo.Student")
Object stu = clz.newInstance();

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public void sayHello(String name) {
// 在运行前根本不知道 name 是什么，只有在运行时 name 才会被确认并打印出来
System.out.println("hello, " + name);
}

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new com.mysql.jdbc.Driver();

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if ( xxx == "mysql") {
new com.mysql.jdbc.Driver();
else if ( xxx == "redis" ) {
new com.redis.jdbc.Driver();
else if ( ... ){
}

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// 反射的方式动态加载类
Class.forName("com.mysql.jdbc.Driver");

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// 1 使用 Class 类的 forName 静态方法
Class.forName(driver);
// 2 直接获取某一个对象的 class
Class<?> cl = int.class;
// 3 调用某个对象的 getClass() 方法
StringBuilder str = new StringBuilder("123");
Class<?> klass = str.getClass();

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public static void displayObjectClass(Object o) {
if (o instanceof Vector)
System.out.println("对象是 java.util.Vector 类的实例");
else if (o instanceof ArrayList)
System.out.println("对象是 java.util.ArrayList 类的实例");
else
System.out.println("对象是 " + o.getClass() + " 类的实例");
}

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Class<?> c = String.class;
Object str = c.newInstance();

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public class ReflectDemo {
public static void main(String[] args) throws IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
Class<?> c = MyClass.class;
Method[] methods = c.getMethods();
Method[] declaredMethods = c.getDeclaredMethods();
Method method = c.getMethod("add", int.class, int.class);
System.out.println("getMethods获取的方法：");
for(Method m:methods)
System.out.println(m);
System.out.println("getDeclaredMethods获取的方法：");
for(Method m:declaredMethods)
System.out.println(m);
}
}
class MyClass {
public int add(int a, int b) {
return a + b;
}
public int sub(int a, int b) {
return a - b;
}
}
// 输出
/*
getMethods获取的方法：
public int com.shuofxz.basic.ReflectDemo$MyClass.add(int,int)
public int com.shuofxz.basic.ReflectDemo$MyClass.sub(int,int)
public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
public final void java.lang.Object.wait() throws java.lang.InterruptedException
public boolean java.lang.Object.equals(java.lang.Object)
public java.lang.String java.lang.Object.toString()
public native int java.lang.Object.hashCode()
public final native java.lang.Class java.lang.Object.getClass()
public final native void java.lang.Object.notify()
public final native void java.lang.Object.notifyAll()
getDeclaredMethods获取的方法：
public int com.shuofxz.basic.ReflectDemo$MyClass.add(int,int)
public int com.shuofxz.basic.ReflectDemo$MyClass.sub(int,int)
*/

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public class ReflectDemo {
public static void main(String[] args) throws IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
Class<?> mc = MyClass.class;
Object obj = mc.newInstance();
//获取methodClass类的add方法
Method method = mc.getMethod("add", int.class, int.class);
//调用method对应的方法 => add(1,4)
Object result = method.invoke(obj, 1, 4);
System.out.println(result);
}
}

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