java 反射小例子

浅浅的花香味﹌ 2022-06-02 11:36 186阅读 0赞

# java 反射小例子 #

先说一下目前我理解的反射。一般情况下，我们使用一个对象的时候，可以直接用类进行初始化一个对象，但是在有些情况下，我们不具备初始化对象的条件。这时候我们就可以使用反射。

下面是一个反射的例子。用于创建一个指定类的对象。

package com.xueyou.demo.reflection;
    
    import com.sun.org.apache.bcel.internal.util.ClassLoader;
    
    public class ReflectApp {
        public static void main(String[] args) {
            Student s = (Student) OptionHelper.instantiateByClassNameAndParameter("com.xueyou.demo.reflection.Student", ClassLoader.getSystemClassLoader(), null, null);
            s.setAge(1);
            System.out.println(s.getAge());
    
            Class<?>[] classtypes = {String.class, int.class};
            Object[] params = new Object[2];
            params[0] = "aaaa";
            params[1] = 13;
            Student s2 = (Student) OptionHelper.instantiateByClassNameAndParameter("com.xueyou.demo.reflection.Student", ClassLoader.getSystemClassLoader(), classtypes, params);
            System.out.println(s2.getAge());
            System.out.println(s2.getName());
        }
    }

package com.xueyou.demo.reflection;
    
    import java.lang.reflect.Constructor;
    import java.lang.reflect.InvocationTargetException;
    
    public class OptionHelper {
    
        public static Object instantiateByClassNameAndParameter(String className, ClassLoader classLoader, Class<?>[] type, Object[] parameter) {
            if (className == null) {
                throw new NullPointerException();
            }
            try {
                Class<?> classObj = null;
                classObj = classLoader.loadClass(className);
                if (type == null) {
                    return classObj.newInstance();
                } else {
                    Constructor<?> constructor = classObj.getConstructor(type);
                    return constructor.newInstance(parameter);
                }
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
                return null;
            } catch (InstantiationException e) {
                e.printStackTrace();
                return null;
            } catch (IllegalAccessException e) {
                e.printStackTrace();
                return null;
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
                return null;
            } catch (InvocationTargetException e) {
                e.printStackTrace();
                return null;
            }
        }
    }

package com.xueyou.demo.reflection;
    
    public class Student {
        private String name;
        private int age;
    
        public Student() {
        }
    
        public Student(String name, int age) {
            this.name = name;
            this.age = age;
        }
    
        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;
        }
    }

运行结果：

![Center][]

[Center]: /images/20220602/ddb5b415f0b14029b02fb3895a9bf3ba.png