Java Foundation Consolidation Series (iii): Field class for member variable reflection

To use reflection, you first need to get the class object for the Class class object. A Field object corresponds to the attribute (member variable) information of a reflection class

There is a method in this field.setaccessible (Boolean b), this method is very important, there is a comment in the code, is used to improve the speed of Java reflection.

First, we need to define a javabean that the bean uses as our reflection class:

<span style= "Font-family:microsoft yahei;font-size:12px;" >package Com.test;public class Point {private int x;public int y;public point (int x,int y) {super (); this.x = X;this.y = y;}} </span>

we then write a concrete reflection method in main:

<span style= "Font-family:microsoft yahei;font-size:12px;" >package Com.test;import Java.lang.reflect.field;public class Reflecttest {public static void main (String []args) Throws Exception{point pt1 = new Point (3, 5);//The resulting fieldy here is a field on the class (member variable), not the value of Y on instance pt1 field Fieldy = Pt1.getclass (). GetField ("Y"); System.out.println (Fieldy); Output result: public int com.test.Point.yint num = fieldy.getint (PT1); Here you get the value of the variable y above the PT1 instance System.out.println (num); Output: 5//because the member variable x is private, the method as above is not able to get the value of X//Because we need to use the violent reflex field FIELDX = Pt1.getclass (). Getdeclaredfield ("X"); The Getdeclaredfield () method here is to get the field on the class, whether public or private fieldx.setaccessible (true),/** sets the accessible flag of this object to the indicated Boolean value. A value of TRUE indicates that the reflected object should cancel the Java language access check when it is used. A value of false indicates that the reflected object should implement a Java language access check. *///ps:setaccessible is a switch that enables and disables access security checks, is not true to be able to access false and cannot access/through Setaccessible (true) System.out.println (Fieldx.get (PT1)) to improve the reflex speed by closing the security check;}} </span> 

Note that the Setaccessible () method is used when reflecting on the class private member variable x above, which has a specific explanation in the code.

We make a small reflection of the plum, that is, by reflection technology to the string in another class member variable characters in the ' B ' the change to ' A '

<span style= "Font-family:microsoft yahei;font-size:12px;" >package Com.test;public class Point {public String s1= ' Ball ';p ublic string s2 = "Basketball";p ublic string s3= "Lipengl Ong ";} </span>

Below is the main function

<span style= "Font-family:microsoft yahei;font-size:12px;" >package Com.test;import Java.lang.reflect.field;public class Reflecttest {public static void main (String []args) Throws Exception{point pt1 = new Point ();//First Get all methods of a Field array field[] fields = Pt1.getclass (). GetFields (); For (field Field:fields) {///first to determine whether the resulting type is stringif (field.gettype () = = String.class) {//assigns the original variable value to oldvaluestring OldValue = (String Field.get (PT1);//Convert the character in OldValue to character B to astring newvalue = Oldvalue.replace (' B ', ' a ');//Assign a new value to Pt1 Field.set (PT1, newvalue);}} System.out.println (PT1.S1); System.out.println (PT1.S2); System.out.println (PT1.S3);}} </span>

The results are as follows:

Aall
Aasketaall
Lipenglong

Java Foundation Consolidation Series (iii): Field class for member variable reflection