一、反射(主要用于框架的开发)反射加载类并允许以编程的方式解剖类中的各种成分成员变量、方法、构造器等1、反射第一步加载类获取类的字节码Class对象获取Class对象的三种方式Class c1 类名.class调用Class提供方法public static Class forName(String package);Object提供的方法public Class getClass(); Class c3 对象.getClass();public class Test { public static void main(String[] args) throws ClassNotFoundException { Class s1 Student.class; System.out.println(s1.getName()); //全类名 System.out.println(s1.getSimpleName()); // 简名 Class s2 Class.forName(com.itrus.study.reflect.Student); System.out.println(s1 s2); Student student new Student(); Class s3 student.getClass(); System.out.println(s1 s3); } }2.获取类的构造器public class Student { private String name; private Student() { } public Student(String name) { this.name name; } }1.获取public修饰的所有构造器public class Test2 { public static void main(String[] args) { Class s Student.class; Constructor[] constructors s.getConstructors(); for (Constructor constructor : constructors) { System.out.println(constructor.getName() - constructor.getParameterCount()); } } }2.获取所有构造器public class Test2 { public static void main(String[] args) { Class s Student.class; Constructor[] constructors s.getDeclaredConstructors(); for (Constructor constructor : constructors) { System.out.println(constructor.getName() - constructor.getParameterCount()); } } }3.获取一个指定的public修饰的构造器import java.lang.reflect.Constructor; public class Test2 { public static void main(String[] args) throws NoSuchMethodException { Class s Student.class; Constructor constructor s.getConstructor(String.class, int.class); System.out.println(constructor.getName() - constructor.getParameterCount()); } }4.获取一个指定的任意构造器public class Test2 { public static void main(String[] args) throws NoSuchMethodException { Class s Student.class; Constructor constructor s.getDeclaredConstructor(); System.out.println(constructor.getName() - constructor.getParameterCount()); } }3.获取类构造器的作用使用newInstance直接创建对象可能会因为检查访问权限而导致创建失败但是如果把accessible设置为true即使是private修饰的私有构造方法也可以构造对象public class Student { private String name; private int age; private Student() { System.out.println(初始化了一个对象); } public Student(String name, int age) { this.name name; this.age age; } public Student(String name) { this.name name; } }public class Test2 { public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException { Class s Student.class; Constructor constructor s.getDeclaredConstructor(); System.out.println(constructor.getName() - constructor.getParameterCount()); // cannot access a member of class com.itrus.study.reflect.Student with modifiers private //Student student (Student) constructor.newInstance(); constructor.setAccessible(true); Student student (Student) constructor.newInstance(); } }4.获取类的成员变量package com.itrus.study.reflect; public class Student { private static int a; public static final String str 你好世界; private String name; private int age; private Student() { System.out.println(初始化了一个对象); } public Student(String name, int age) { this.name name; this.age age; } public Student(String name) { this.name name; } }public class Test3 { public static void main(String[] args) throws NoSuchFieldException { Class student Student.class; //获取public修饰的所有属性 Field[] fields student.getFields(); for(Field field : fields) { System.out.println(field.getName() --- field.getType()); } System.out.println(); //获取所有属性 fields student.getDeclaredFields(); for(Field field : fields) { System.out.println(field.getName() --- field.getType()); } System.out.println(); //获取指定public成员变量 Field fstr student.getField(str); System.out.println(fstr.getName() --- fstr.getType()); System.out.println(); //获取指定成员变量 Field fage student.getDeclaredField(age); System.out.println(fage.getName() --- fage.getType()); System.out.println(); } }5.获取类成员变量的作用//给成员变量赋值 Student s new Student(); fage.setAccessible(true); fage.set(s, 20); System.out.println(s); int age (int) fage.get(s); System.out.println(age);6.获取成员方法getMethods会获取当前类和所有父类的public修饰的方法而getDeclaredMethods方法是获取当前类的所有方法package com.itrus.study.reflect; public class Student { private static int a; public static final String str 你好世界; private String name; private int age; public Student() { System.out.println(初始化了一个对象); } private String eat() { return 吃饭; } public String getName() { return name; } public void setName(String name) { this.name name; } public Student(String name, int age) { this.name name; this.age age; } public Student(String name) { this.name name; } Override public String toString() { return Student{ name name \ , age age }; } }public class Test4 { public static void main(String[] args) throws NoSuchMethodException { Class c Student.class; Method[] methods c.getMethods(); for (Method method : methods) { System.out.println(method.getName() --- method.getParameterCount() --- method.getReturnType()); } System.out.println(); methods c.getDeclaredMethods(); for (Method method : methods) { System.out.println(method.getName() --- method.getParameterCount() --- method.getReturnType()); } System.out.println(); Method method c.getMethod(setName, String.class); System.out.println(method.getName() --- method.getParameterCount() --- method.getReturnType()); System.out.println(); method c.getDeclaredMethod(setName, String.class); System.out.println(method.getName() --- method.getParameterCount() --- method.getReturnType()); System.out.println(); } }7.获取成员方法的作用Student s new Student(); method.setAccessible(true); method.invoke(s, 张三); System.out.println(s.getName());