反射基础

作者: 陈柴盐 | 来源:发表于2018-11-26 23:40 被阅读0次

材料准备

public class Student {

            private int id;
            private String name;
            private int age;

            public Student(int id, String name, int age) {
                this.id = id;
                this.name = name;
                this.age = age;
            }


            public Student(String name) {
                this.name = name;
            }

            public Student() {
            }

            public int getId() {
                return id;
            }

            public void setId(int id) {
                this.id = id;
            }

            public String getName() {
                return name;
            }

            public void setName(String name) {
                this.name = name;
            }

            public int getAge() {
                return age;
            }

            public void setAge(int age) {
                this.age = age;
            }

            @Override
            public String toString() {
                return "Student{" +
                        "id=" + id +
                        ", name='" + name + '\'' +
                        ", age=" + age +
                        '}' + "\n";
            }


            @Override
            public boolean equals(Object o) {
                if (this == o) {return true;}
                if (o == null || getClass() != o.getClass()) {return false;}

                Student student = (Student) o;

                if (id != student.id) {return false;}
                if (age != student.age) {return false;}
                return name != null ? name.equals(student.name) : student.name == null;
            }

            @Override
            public int hashCode() {
                int result = id;
                result = 31 * result + (name != null ? name.hashCode() : 0);
                result = 31 * result + age;
                return result;
            }


            /*方法*/
        public void method1(String string) {
            System.out.println(string);
        }

        public void method2(String string,int i) {
            System.out.println(string+i);
        }

        public void method3(String string,Integer integer,String s) {
            System.out.println(string+integer+s);
        }
}

Class类

获取Class对象

通过类名.class获取

通过对象名.getClass()获得

通过Class类的静态方法forName("类全名字符串")获得

Class c1 = Student.class;

Student s =  new Student();
Class c2 = s.getClass();

Class c3 = Class.forName("xxx.Student");

Constructor类

类中的每一个构造方法都是一个Constructor类的对象

通过Class对象获取Constructor对象

Constructor getConstructor(Class... parameterTypes)//根据参数获取构造器

Constructor[] getConstructors()//获取所有的构造方法

常用方法

T newInstance(Object... initargs)//创建对象

代码示例:

public static void main(String[] args) throws Exception {
        Class<Student> studentClass = Student.class;

        //获取无参构造方法
        Constructor<Student> constructor = studentClass.getConstructor();
        System.out.println("constructor = " + constructor);
        Student student = constructor.newInstance();
        System.out.println("student = " + student);
        System.out.println("=============================");
    
        //获取有参构造方法
        Constructor<Student> constructor1 = studentClass.getConstructor(String.class);
        System.out.println("constructor1 = " + constructor1);
        Student student1 = constructor1.newInstance("权属");
        System.out.println("student1 = " + student1);
        System.out.println("=============================");
    
        //获取有参构造方法2
        Constructor<Student> constructor2 = studentClass.getConstructor(int.class, String.class, int.class);
        System.out.println("constructor2 = " + constructor2);
        Student student2 = constructor2.newInstance(1, "内容", 18);
        System.out.println(student2);
        System.out.println("=============================");
    
        //获取所有构造方法
        Constructor<?>[] constructors = studentClass.getConstructors();
        for (Constructor<?> subConstructor : constructors) {
            System.out.println(subConstructor);
        }

    }

输出结果

constructor = public junit和反射和注解.反射.Student()
student = Student{id=0, name='null', age=0}

=============================
constructor1 = public junit和反射和注解.反射.Student(java.lang.String)
student1 = Student{id=0, name='权属', age=0}

=============================
constructor2 = public junit和反射和注解.反射.Student(int,java.lang.String,int)
Student{id=1, name='内容', age=18}

=============================
public junit和反射和注解.反射.Student()
public junit和反射和注解.反射.Student(java.lang.String)
public junit和反射和注解.反射.Student(int,java.lang.String,int)

Method类

类中每一个成员方法都是一个Method对象

通过Class对象获取Method对象

Method getMethod(String methodName, Class...param)//根据方法名和参数获取方法对象

Method[] getMethods()//获取所有方法对象

Method[] getDeclaredMethods()//获取不包括父类方法的独享

method类的常用方法

Object invoke(Object obj,Object...args)

代码示例:

    public static void main(String[] args) throws Exception{
        Class<Student> studentClass = Student.class;

        Method method1 = studentClass.getMethod("method1", String.class);
        Method method2 = studentClass.getMethod("method2", String.class, int.class);
        Method method3 = studentClass.getMethod("method3", String.class, Integer.class, String.class);

        method1.invoke(studentClass.getConstructor().newInstance(), "你");
        method2.invoke(studentClass.getConstructor().newInstance(), "我", 1);
        method3.invoke(studentClass.getConstructor().newInstance(),"他",1,"们");

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

        Method[] methods = studentClass.getMethods();
        for (Method method : methods) {
            System.out.println(method);
        }

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

        //不包括父类的方法
        Method[] declaredMethods = studentClass.getDeclaredMethods();
        for (Method declaredMethod : declaredMethods) {
            System.out.println(declaredMethod);
        }
    }

输出结果

你
我1
他1们
=============================
public void exercise.Student.setAge(int)
public void exercise.Student.setId(int)
public int exercise.Student.getAge()
public void exercise.Student.method2(java.lang.String,int)
public void exercise.Student.method1(java.lang.String)
public void exercise.Student.method3(java.lang.String,java.lang.Integer,java.lang.String)
......

Field类

类中的每一个成员变量都是一个Field对象

Class对象中获取Field对象的方法

Field getDeclaredField(String name);//根据变量名获取对应的Field对象

Field[] getDeclaredFields();//获取所有的Field对象

Field类的常用方法
void set(Object obj, Object value)
void setInt(Object obj, int i)
void setLong(Object obj, long l)
void setBoolean(Object obj, boolean z)
void setDouble(Object obj, double d)

Object get(Object obj)
int getInt(Object obj)
long getLong(Object obj)
boolean getBoolean(Object ob)
double getDouble(Object obj)

private修饰的变量需要设置setAccessible(true)才可以反射设置属性值

void setAccessible(true);
* 设置是否取消权限检查
true：取消，不检查权限

false:不取消，要检查权限，默认值

暴力反射，设置为可以直接访问私有类型的属性。

代码示例

public static void main(String[] args) throws Exception{

        //Class对象是放在方法区(性质跟常量池像的那个,方法区包含常量池)
        Class<Student> studentClass = Student.class;

        Field age = studentClass.getDeclaredField("name");
        Student student = studentClass.getConstructor().newInstance();
        System.out.println("studentBefore = " + student);
        age.setAccessible(true);
        age.set(student,"one");
        System.out.println("studentAfter = " + student);

        Field[] fields = studentClass.getDeclaredFields();
        for (Field field : fields) {
            field.setAccessible(true);
            if (field.getType()==int.class) {
                System.out.println("属性是整型");
            }else if(field.getType()==String.class){
                System.out.println("属性是String类型");
            }
        }
    }

输出结果

studentBefore = Student{id=0, name='null', age=0}

studentAfter = Student{id=0, name='one', age=0}

属性是整型
属性是String类型
属性是整型

Annotation类

类中每一个注解都是Annotation的子类

AnnotatedElement接口,定义了获取注解信息的方法

Class，Constructor，Method，Field等类都实现了AnnotatedElement接口

Annotation接口的方法:

T getAnnotation(Class<T> annotationClass)//根据注解类型获取注解对象那个

Annotation[] getAnnotations()//获取所有注解对象,可以获父类上注解对象,前提标注元注解@Inherited

Annotation[] getDeclaredAnnotations()//获取所有注解对象,仅限本类中的

boolean isAnnotationPresent(Class annotationClass)//判断是否使用了某个注解

获取注解对象的方法:

注解作用在哪个成员上就获得该成员对应的对象获得注解信息

比如:注解作用在类上,那么应该通过Class对象的getAnnotation(Class<T> annotationClass)方法获取

注解作用在方法上,那么应该通过Method对象的getAnnotation(Class<T> annotationClass)方法

构造器和Field同理

反射基础

材料准备

Class类

Constructor类

Method类

Annotation类

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