Java反射

反射是在运行时动态访问类与对象的技术，大多数框架都基于反射实现参数设置，动态注入等。

反射的四个核心类

　Class、Constructor、Method、Field

Class核心方法

 

员工实体类Employee

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package com.imooc.reflect.entity;

/**
 * 员工实体类
 */
public class Employee {
    static {
        System.out.println("Employee类已被加载到jvm,并已初始化");
    }
    private Integer eno;
    public String ename;
    private Float salary;
    private String dname;

    public Employee(){
        System.out.println("Employee默认构造方法已被执行");
    }

    public Employee(Integer eno,String ename,Float salary , String dname){
        this.eno = eno;
        this.ename = ename;
        this.salary = salary;
        this.dname = dname;
        System.out.println("Employee带参构造方法已被执行");
    }

    public Integer getEno() {
        return eno;
    }

    public void setEno(Integer eno) {
        this.eno = eno;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public Float getSalary() {
        return salary;
    }

    public void setSalary(Float salary) {
        this.salary = salary;
    }

    public String getDname() {
        return dname;
    }

    public void setDname(String dname) {
        this.dname = dname;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "eno=" + eno +
                ", ename='" + ename + '\'' +
                ", salary=" + salary +
                ", dname='" + dname + '\'' +
                '}';
    }

    public Employee updateSalary(Float val){
        this.salary = (Float) (this.salary + val);
        System.out.println(this.ename + "调薪至" + this.salary + "元");
        return this;
    }
}
Employee
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package com.imooc.reflect;

import com.imooc.reflect.entity.Employee;

public class ClassSample {
    public static void main(String[] args) {
        try {
            //Class.forName()方法将指定的类加载到jvm,并返回对应Class对象
            Class employeeClass = Class.forName("com.imooc.reflect.entity.Employee");
            System.out.println("Employee已被加载到jvm");
            //newInstance通过默认构造方法创建新的对象
            Employee emp = (Employee)employeeClass.newInstance();
            System.out.println(emp);
        } catch (ClassNotFoundException e) {
            //类名与类路径书写错误是抛出"类无法找到"异常
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            //非法访问异常,当在作用域外访问对象方法或成员变量时抛出
            e.printStackTrace();
        } catch (InstantiationException e) {
            //对象无法被实例化,抛出"实例化异常"
            e.printStackTrace();
        }
    }
}
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Constructor类核心方法

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package com.imooc.reflect;

import com.imooc.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

/**
 * 利用带参构造方法创建对象
 */
public class ConstructorSample {
    public static void main(String[] args) {
        try {
            Class employeeClass = Class.forName("com.imooc.reflect.entity.Employee");
            Constructor constructor = employeeClass.getConstructor(new Class[]{
                    Integer.class,String.class,Float.class,String.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    100,"李磊",3000f,"研发部"
            });
            System.out.println(employee);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            //没有找到与之对应格式的方法
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            //当被调用的方法的内部抛出了异常而没有被捕获时
            e.printStackTrace();
        }
    }
}
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Method类核心方法

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package com.imooc.reflect;

import com.imooc.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * 利用Method方法类调用
 */
public class MethodSample {
    public static void main(String[] args) {
        try {
            Class employeeClass = Class.forName("com.imooc.reflect.entity.Employee");
            Constructor constructor = employeeClass.getConstructor(new Class[]{
                    Integer.class,String.class,Float.class,String.class
            });
            Employee employee = (Employee)constructor.newInstance(new Object[]{
                    100,"李磊",3000f,"研发部"
            });
            Method updateSalaryMethod = employeeClass.getMethod("updateSalary" , new Class[]{Float.class});
            Employee employee1 = (Employee)updateSalaryMethod.invoke(employee,new Object[]{1000f});
            System.out.println(employee1);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}
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Field类核心方法

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package com.imooc.reflect;

import com.imooc.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;

/**
 * 利用Field对成员变量赋值/取值
 */
public class FieldSample {
    public static void main(String[] args) {
        try {
            Class employeeClass = Class.forName("com.imooc.reflect.entity.Employee");
            Constructor constructor = employeeClass.getConstructor(new Class[]{
                    Integer.class,String.class,Float.class,String.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    100,"李磊",3000f,"研发部"
            });
            Field enameField = employeeClass.getField("ename");
            enameField.set(employee,"李雷");
            String ename = (String)enameField.get(employee);
            System.out.println("ename:" + ename);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (NoSuchFieldException e) {
            //没有找到对应成员变量时抛出的异常
            e.printStackTrace();
        }
    }
}
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 getDecared系列方法获取对象不用考虑public或private

使用getDecaredFields()获取所有成员变量

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package com.imooc.reflect;

import com.imooc.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * 获取对象所有成员变量值
 */
public class getDeclaredSample {
    public static void main(String[] args) {
        try {
            Class employeeClass = Class.forName("com.imooc.reflect.entity.Employee");
            Constructor constructor = employeeClass.getConstructor(new Class[]{
                    Integer.class, String.class, Float.class, String.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    100, "李磊", 3000f, "研发部"
            });
            //获取当前类所有成员变量
            Field[] fields = employeeClass.getDeclaredFields();
            for(Field field : fields){
//                System.out.println(field.getName());
                if(field.getModifiers() == 1){ //pubilc修饰
                    Object val = field.get(employee);
                    System.out.println(field.getName() + ":" + val);
                }else if(field.getModifiers() == 2){ //private修饰
                    String methodName = "get" + field.getName().substring(0,1).toUpperCase()
                                        + field.getName().substring(1);
                    Method getMethod = employeeClass.getMethod(methodName);
                    Object ret = getMethod.invoke(employee);
                    System.out.println(field.getName() + ":" + ret);
                }
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}
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posted @   南风知君  阅读(42)  评论(0)  编辑  收藏  举报
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