setAccessible()方法

dping — Fri, 20 Jul 2012 05:51:00 GMT

java.lang.IllegalAccessException:
Class com.test.accessible.Main
can not access
a member of class com.test.accessible.AccessibleTest
with modifiers "private"

java代码中，常常将一个类的成员变量置为private
在类的外面获取此类的私有成员变量的value时，需要注意:
测试类：

public class AccessibleTest {

    private int id;
    private String name;

    public AccessibleTest() {

    }

    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;
    }

}

Main类：

public class Main {

    public static void main(String[] args) throws Exception {
        Class clazz = Class.forName("com.test.accessible.AccessibleTest");
        AccessibleTest at = new AccessibleTest();
        at.setId(1);
        at.setName("AT");
        for (Field f : clazz.getDeclaredFields()) {
            f.setAccessible(true);//AccessibleTest类中的成员变量为private,故必须进行此操作
            System.out.println(f.get(at));//获取当前对象中当前Field的value
        }

    }

}

如果没有在获取private的Field之前调用setAccessible(true)方法，异常：

java.lang.IllegalAccessException:
Class com.test.accessible.Main
can not access
a member of class com.test.accessible.AccessibleTest
with modifiers "private"

当然在AccessibleTest类的内部(AccessibleTest的内部类除外)

进行如上操作则不需要调用setAccesible()方法

**另外：由于Accessible的值为 true 则指示反射的对象在使用时应该取消 Java 语言访问检查。
值为 false 则指示反射的对象应该实施 Java 语言访问检查。
将其设为true，可以提高java反射速度

dping 2012-07-20 13:51 发表评论

java.lang.Class.getDeclaredField(String fieldName)

dping — Fri, 20 Jul 2012 05:01:00 GMT

转自：http://technet.microsoft.com/zh-cn/library/aa989722

功能：Gets the field (public, private, or protected) with the given name.

原型：public java.lang.reflect.Field getDeclaredField(java.lang.String fieldName)

Example:

// class_getdeclaredfield.jsl

import java.lang.reflect.Field;
import java.util.Date;

public class Program
{
    public static void main(String[] args)
    {
        try
        {
            // Get the Class object associated with this class.
            Program program = new Program();
            Class progClass = program.getClass();

            // Get the field named str.
            Field strField = progClass.getDeclaredField("str");
            System.out.println("Field found: " + strField.toString());

            // Get the field named date.
            Field dateField = progClass.getDeclaredField("date");
            System.out.println("Field found: " + dateField.toString());

            // Get the field named i.
            Field iField = progClass.getDeclaredField("i");
            System.out.println("Field found: " + iField.toString());
        }
        catch (NoSuchFieldException ex)
        {
            System.out.println(ex.toString());
        }
    }

    public Program()
    {
    }

    public Program(String str, Date date, int i)
    {
        this.str = str;
        this.date = date;
        this.i = i;
    }

    public String str = "Hello";
    private Date date = new Date();
    protected int i = 0;
}

/*
Output:
Field found: public java.lang.String Program.str
Field found: private java.util.Date Program.date
Field found: protected int Program.i
*/

注： getFields()获得某个类的所有的公共（public）的字段，包括父类。
getDeclaredFields()获得某个类的所有申明的字段，即包括public、private和proteced，但是不包括父类的申明字段。

dping 2012-07-20 13:01 发表评论

C++博客-dping

setAccessible()方法

java.lang.Class.getDeclaredField(String fieldName)