实例讲解Java基础之反射

前期准备

编写一个真实类phone,实现list接口

public class Phone implements List {
  public double price;
  public String name;
  public Phone() {
  }
  public Phone(double price, String name) {
    this.price = price;
    this.name = name;
  }
  public double getPrice() {
    return price;
  }
  public void gege(String h){
    System.out.println("gege的"+h);
  }
  public void setPrice(double price) {
    this.price = price;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  @Override
  public String toString() {
    return "Phone{" +
        "price=" + price +
        ", name='" + name + '\'' +
        '}';
  }
  @Override
  public int size() {
    return 0;
  }
  @Override
  public boolean isEmpty() {
    return false;
  }
  @Override
  public boolean contains(Object o) {
    return false;
  }
  @Override
  public Iterator iterator() {
    return null;
  }
  @Override
  public Object[] toArray() {
    return new Object[0];
  }
  @Override
  public boolean add(Object o) {
    return false;
  }
  @Override
  public boolean remove(Object o) {
    return false;
  }
  @Override
  public boolean addAll(Collection c) {
    return false;
  }
  @Override
  public boolean addAll(int index, Collection c) {
    return false;
  }
  @Override
  public void clear() {
  }
  @Override
  public Object get(int index) {
    return null;
  }
  @Override
  public Object set(int index, Object element) {
    return null;
  }
  @Override
  public void add(int index, Object element) {
  }
  @Override
  public Object remove(int index) {
    return null;
  }
  @Override
  public int indexOf(Object o) {
    return 0;
  }
  @Override
  public int lastIndexOf(Object o) {
    return 0;
  }
  @Override
  public ListIterator listIterator() {
    return null;
  }
  @Override
  public ListIterator listIterator(int index) {
    return null;
  }
  @Override
  public List subList(int fromIndex, int toIndex) {
    return null;
  }
  @Override
  public boolean retainAll(Collection c) {
    return false;
  }
  @Override
  public boolean removeAll(Collection c) {
    return false;
  }
  @Override
  public boolean containsAll(Collection c) {
    return false;
  }
  @Override
  public Object[] toArray(Object[] a) {
    return new Object[0];
  }
}

1.反射之4种new对象

public class Test2 {
  public static void main(String[] args) throws IllegalAccessException, InstantiationException, ClassNotFoundException {
    //第一种
    Phone p = new Phone(2999,"小米");
    System.out.println(p);//Phone{price=2999.0, name='小米'}
    //第二种 需要一个空参构造
    Class<Phone> phoneClass = Phone.class;
    Phone phone = phoneClass.newInstance();
    phone.setName("华为");
    phone.setPrice(3499);
    System.out.println(phone);//Phone{price=3499.0, name='华为'}
    //第三种
    Class<?> aclass = Class.forName("com.demo.bean.Phone");
    Phone p2 = (Phone) aclass.newInstance();
    p2.setPrice(2999);
    p2.setName("魅族");
    System.out.println(p2);//Phone{price=2999.0, name='魅族'}
    //第四种,需要一个配置文件phone.properties
    String name = ResourceBundle.getBundle("phone").getString("myphone");
    Class<?> bClass = Class.forName(name);
    Phone p3 = (Phone) bClass.newInstance();
    p3.setPrice(3299);
    p3.setName("锤子");
    System.out.println(p3);//Phone{price=3299.0, name='锤子'}
  }
}

配置文件phone.properties

myphone=com.demo.bean.Phone

2. 反射之获取类、父类、实现接口

public class Test3 {
  public static void main(String[] args) throws ClassNotFoundException {
    String string = ResourceBundle.getBundle("phone").getString("myphone");
    Class<?> aClass = Class.forName(string);
    //获取类的完整路径
    System.out.println(aClass.getName());//com.demo.bean.Phone
    //获取类的简单名字
    System.out.println(aClass.getSimpleName());//Phone
    //获取类的父类
    Class<?> superclass = aClass.getSuperclass();
    System.out.println(superclass.getName());//java.lang.Object
    System.out.println(superclass.getSimpleName());//Object
    //获得类的接口
    Class<?>[] interfaces = aClass.getInterfaces();
    for (Class<?> in:interfaces
       ) {
      System.out.println(in.getSimpleName());
    }
  }
}

3.反射之获取空参、有参构造

public class Test4 {
  public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException {
    String string = ResourceBundle.getBundle("phone").getString("myphone");
    Class<?> aClass = Class.forName(string);
    //调用的是无参的构造方法
    Phone p1 = (Phone) aClass.newInstance();
    p1.setName("华为");
    p1.setPrice(2999);//Phone{price=2999.0, name='华为'}
    System.out.println(p1);
    //获得无参的构造方法
    Constructor<?> constructor = aClass.getConstructor();
    System.out.println(constructor);//public com.demo.bean.Phone()
    //获得所有的构造方法
    Constructor<?>[] constructors = aClass.getConstructors();
    for (Constructor<?> c:constructors
       ) {
      System.out.println(c);
    }
  }
}

4.反射之获取方法

public class Test5 {
  public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException,InstantiationException,IllegalAccessException,InvocationTargetException{
    String string = ResourceBundle.getBundle("phone").getString("myphone");
    Class<?> aClass = Class.forName(string);
    //包含了父类的方法
    Method[] methods = aClass.getMethods();
    for (Method m:methods
       ) {
      System.out.println(m);
    }
    //本类中的方法，没有父类的方法
    Method[] declaredMethods = aClass.getDeclaredMethods();
    for (Method m:declaredMethods
       ) {
      System.out.println(m);
    }
    Method gege = aClass.getMethod("gege",String.class);
    //获取gege方法的权限修饰符
    System.out.println(Modifier.toString(gege.getModifiers()));
    //获取gege方法的返回值类型
    System.out.println(gege.getReturnType());
    //设置gege的参数值
    Object o = aClass.newInstance();
    gege.invoke(o,"aa");
  }
}

5.反射之获取字段

public class Test6 {
  public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException, InstantiationException {
    String string = ResourceBundle.getBundle("phone").getString("myphone");
    Class<?> aClass = Class.forName(string);
    //只能调用public 字段,但是能得到父类的字段
    Field[] fields = aClass.getFields();
    for (Field f:fields
       ) {
      System.out.println(f.getName());
    }
    //只能调用public 字段，只能得到本类中的字段
    Field[] declaredFields = aClass.getDeclaredFields();
    for (Field f:declaredFields
       ) {
      System.out.println(f.getName());
    }
    //获取某一字段的数据类型
    Field name = aClass.getField("name");
    String simpleName = name.getType().getSimpleName();
    System.out.println(simpleName);
    name.setAccessible(true);
    Object o = aClass.newInstance();
    name.set(o,"华为");
    System.out.println(name.get(o));
  }
}

总结

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