获取类的运行时结构、动态创建对象执行方法

获取类的运行时结构、动态创建对象执行方法 获取类的运行时结构

实体类

package pojo;

public class User {
    private int id;
    private String name;
    private String pwd;
    //构造,有参,无参
    //set/get
    //toString()
    
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + ''' +
                ", pwd='" + pwd + ''' +
                '}';
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public User() {
    }

    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 String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}

获得类的属性和指定属性的值

Class c1 = Class.forName("pojo.User");
System.out.println(c1.getName());//包名+类名 pojo.User
System.out.println(c1.getSimpleName());//类名 User

//获得类的属性
Field[] fields = c1.getFields();//只能找到public属性
for (Field field : fields) {
    System.out.println(field);
}

fields=c1.getDeclaredFields();//获得全部的属性
for (Field field : fields) {
    System.out.println(field);
}
//private int pojo.User.id
//private java.lang.String pojo.User.name
//private java.lang.String pojo.User.pwd

System.out.println("=========================");
//获取指定属性的值
Field name = c1.getDeclaredField("name");
System.out.println(name);
//private java.lang.String pojo.User.name

获取类的方法和指定方法

Class c1 = Class.forName("pojo.User");
//获取类的方法
Method[] methods = c1.getMethods();//获得本类及其父类的全部public方法
for (Method method : methods) {
    System.out.println(method);
}
//public java.lang.String pojo.User.toString()
//public java.lang.String pojo.User.getName()
//public int pojo.User.getId()
//public void pojo.User.setName(java.lang.String)
//public java.lang.String pojo.User.getPwd()
//public void pojo.User.setPwd(java.lang.String)
//public void pojo.User.setId(int)
//public final void java.lang.Object.wait() throws java.lang.InterruptedException
//public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
//public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
//public boolean java.lang.Object.equals(java.lang.Object)
//public native int java.lang.Object.hashCode()
//public final native java.lang.Class java.lang.Object.getClass()
//public final native void java.lang.Object.notify()
//public final native void java.lang.Object.notifyAll()

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

methods=c1.getDeclaredMethods();//获取本类的所有方法
for (Method method : methods) {
    System.out.println(method);
}
//public java.lang.String pojo.User.toString()
//public java.lang.String pojo.User.getName()
//public int pojo.User.getId()
//public void pojo.User.setName(java.lang.String)
//public java.lang.String pojo.User.getPwd()
//public void pojo.User.setPwd(java.lang.String)
//public void pojo.User.setId(int)
System.out.println("==============");
//获得指定方法
Method getName = c1.getMethod("getName", null);
Method setName = c1.getMethod("setName", String.class);
System.out.println(getName);//public java.lang.String pojo.User.getName()
System.out.println(setName);//public void pojo.User.setName(java.lang.String)

获得构造器和指定构造器

Class c1 = Class.forName("pojo.User");
    Constructor[] constructors = c1.getConstructors();//获得public构造器
    for (Constructor constructor : constructors) {
        System.out.println(constructor);
    }
    //public pojo.User()
    //public pojo.User(int,java.lang.String,java.lang.String)
    System.out.println("===========");

    constructors=c1.getDeclaredConstructors();//获得全部构造器
    for (Constructor constructor : constructors) {
        System.out.println(constructor);
    }
    //public pojo.User()
    //public pojo.User(int,java.lang.String,java.lang.String)

    //获得指定构造器
    Constructor constructor = c1.getConstructor(int.class, String.class, String.class);
    System.out.println(constructor);
    //public pojo.User(int,java.lang.String,java.lang.String)
}

动态创建对象执行方法 构造一个对象、通过构造器创建对象、通过反射调用普通方法、通过反射 *** 作属性

Class c1 = Class.forName("pojo.User");

    //构造一个对象
    User user = (User) c1.newInstance();//调用的无参构造器
    System.out.println(user);//User{id=0, name='null', pwd='null'}

    //通过构造器创建对象
    Constructor constructor = c1.getConstructor(int.class, String.class, String.class);
    User user1 = (User) constructor.newInstance(1, "zb", "123");
    System.out.println(user1);//User{id=1, name='zb', pwd='123'}

    //通过反射调用普通方法
    User user2 = (User) c1.newInstance();
    Method setName = c1.getDeclaredMethod("setName", String.class);
    setName.invoke(user2,"zb");
    System.out.println(user2.getName());//zb

    //通过反射 *** 作属性
    User user3 = (User) c1.newInstance();
    Field name = c1.getDeclaredField("name");
    //不能直接 *** 作private的成员，需要关闭安全监测(方法、属性和构造器都有setAccessible方法)
    name.setAccessible(true);
    name.set(user3,"zbzb");
    System.out.println(user3.getName());//zbzb
}