Solved

Traverse Members of a java class

Posted on 2004-09-07
14
300 Views
Last Modified: 2006-11-17
Is it possible to generically traverse through a list members in  a class and store their values in a string

eg

Class test
{
         String  a = " hello ";
         String  b = "world ";
}

The solution would be a function called test.writemem which would traverse through the members and return "Hello world"  without calling the members by name.(saying String = a + b;)

0
Comment
Question by:seanfurlong
  • 5
  • 5
  • 3
  • +1
14 Comments
 
LVL 18

Accepted Solution

by:
armoghan earned 500 total points
ID: 12003494
Yes you can use reflection for it
0
 
LVL 92

Expert Comment

by:objects
ID: 12003499
Use reflection

Class c = test.class;
Field[] fileds = c.getDeclaredFields();

the order is indeterminate though.
0
 
LVL 18

Expert Comment

by:armoghan
ID: 12003503
public class Test2 {
  public static void main(String args[])
    throws Exception {
    Field f;
   
    f = test .class.getField("a");
    System.out.println("" + f);

    f = test .class.getField("b");
    System.out.println(""+ f);
  }
}
0
 
LVL 18

Expert Comment

by:armoghan
ID: 12003506
0
 
LVL 18

Expert Comment

by:armoghan
ID: 12003547
This piece of code works

final Field fields[] =
   final Field fields[] =     test .class.getDeclaredFields();
    for (int i = 0; i < fields.length; ++i) {
   
        test fieldTest = new test ();
        Field f = fields[i];
        f.setAccessible(true);
        try {
          System.out.println(f.get(fieldTest));
        }
        catch (IllegalAccessException ex) {
        }
        catch (IllegalArgumentException ex) {
        }
    }
0
 

Expert Comment

by:Emilda
ID: 12004224
Try this:

import java.lang.reflect.Field;

public class TestFields {
   String  a = " hello ";
   String  b = "world ";

  public static void main(String[] args) {
    TestFields test = new TestFields();
    try {
           String values = test.writemem();              
           System.out.println(values);
    } catch (IllegalAccessException e) {
    }
  }
  public String writemem() throws IllegalAccessException {
    Field[] fields = TestFields.class.getDeclaredFields();
    String values = new String();
          
    for(int i=0; i<fields.length; i++) {                
          String name =  fields[i].getName();
          if(name.indexOf("class") == -1) {
             String value = fields[i].get(this).toString();
             values = values + value;
          }                
    }
    return values;
  }
}

0
 
LVL 1

Expert Comment

by:softengg
ID: 12004621
This program will print the fields as u have asked. Output of the following programs on console is "hello world  under world"

package untitled1;

import java.lang.reflect.*;
import java.awt.*;

public class Untitled1 {
  public String a = "hello";
  public String b = "world";
  public String c = " under world";
  public Untitled1() {
  }

  public static void main(String[] args) {
    Untitled1 u = new Untitled1();
    Rectangle r = new Rectangle(100, 325);
    u.me(u.getClass());
  }

  void me(Class c) {
    Field heightField;
    Field field;
    Integer heightValue;
    StringBuffer buf = new StringBuffer();
    try {
      Field[] publicFields = c.getFields();
      for (int i = 0; i < publicFields.length; i++) {
        field = publicFields[i];
        String fieldName = publicFields[i].getName();
        String value = (String) field.get(this);
        buf.append(value);
        buf.append(" ");
      }
    }
    catch (SecurityException e) {
      System.out.println(e);
    }
    catch (IllegalAccessException e) {
      System.out.println(e);
    }
    System.out.println(buf.toString());

  }

}
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 

Expert Comment

by:Emilda
ID: 12012331
getFields() returns only the public fields.
0
 
LVL 1

Expert Comment

by:softengg
ID: 12013606
The requiremnt is not to list private fields.
0
 

Expert Comment

by:Emilda
ID: 12013629
See the class given in the question. The fields given inside that doesn't have the public identifier.
0
 
LVL 1

Expert Comment

by:softengg
ID: 12014598
Here is the modified code: this will print all variables, public, private, and package level in a class.


package untitled1;

import java.lang.reflect.*;
import java.awt.*;

public class Untitled1 {
  public String a = "hello";
  public String b = "world";
  private String c = " under world";
  public Untitled1() {
  }

  public static void main(String[] args) {
    Untitled1 u = new Untitled1();
    Rectangle r = new Rectangle(100, 325);
    u.me(u.getClass());
  }

  void me(Class c) {
    Field heightField;
    Field field;
    Integer heightValue;
    StringBuffer buf = new StringBuffer();
    try {
      Field[] publicFields = c.getDeclaredFields();
      for (int i = 0; i < publicFields.length; i++) {
        field = publicFields[i];
        String fieldName = publicFields[i].getName();
        String value = (String) field.get(this);
        buf.append(value);
        buf.append(" ");
      }
    }
    catch (SecurityException e) {
      System.out.println(e);
    }
    catch (IllegalAccessException e) {
      System.out.println(e);
    }
    System.out.println(buf.toString());

  }

}
0
 
LVL 1

Expert Comment

by:softengg
ID: 12014603
The last code posted by me will print this our put.

hello world  under world

U can verify this.
0
 
LVL 1

Expert Comment

by:softengg
ID: 12023972
Dear seanfurlong, COnfirm me that the code pasted by me is working or not. I have tested and it is printing all the members of the class i.e. private, public and package level with their values.
0
 
LVL 18

Expert Comment

by:armoghan
ID: 12186721
thanx :)
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
java  and programming certification ? 4 86
ArrayIndexOutOfBoundException 9 68
print map entry 34 55
reverse digits of a number using for loop 5 36
INTRODUCTION Working with files is a moderately common task in Java.  For most projects hard coding the file names, using parameters in configuration files, or using command-line arguments is sufficient.   However, when your application has vi…
After being asked a question last year, I went into one of my moods where I did some research and code just for the fun and learning of it all.  Subsequently, from this journey, I put together this article on "Range Searching Using Visual Basic.NET …
Viewers will learn about the regular for loop in Java and how to use it. Definition: Break the for loop down into 3 parts: Syntax when using for loops: Example using a for loop:
This video teaches viewers about errors in exception handling.

895 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

13 Experts available now in Live!

Get 1:1 Help Now