Iterating through Parameter Array - Java Reflection

Question

I am new to java and am not able to figure out why the second way to iterate through parameters throws an exception. Interestingly param !=null passes however i get ArrayIndexOutofBounds exception later. I looked at following link. but that's not helping me. Iterating through method parameters

import java.lang.reflect.*;

public class TestReflection {

    public static void main(String[] args) {
    Class<ReflectThis> c = (Class<ReflectThis>)ReflectThis.class;
    System.out.println("public class " + c.getName());
    System.out.println("{");
    Method methods[] = c.getMethods();
    for(Method m : methods)
    {
        if(m.isAccessible())
            System.out.print("    public ");
        else
            System.out.print("    private ");

            System.out.print(m.getName()+"(");
        //System.out.println("Parameteres");
        Parameter[] params = null;
        params = m.getParameters();
            //method 1 for iterating thr params
        for(Parameter p : params)
        {
            if(p ==  null)
                break;
            System.out.print(p.getType()+ " " +p.getName()+",");

        }
        params = m.getParameters();
            //method 2 for iterating thr params
    if(params != null)
        {
            for(int i=0; params[i] != null; i++)
            {
                System.out.print(params[i].getType()+ " " +params[i].getName());
                if(params[i+1] != null)
                    System.out.print(", ");
            }
        }
        System.out.println(");");
    }

    System.out.println("}");

    }

}

score 2 · Accepted Answer · edited May 23 '17 at 10:32

2

You're simply looping out of bounds.

 for(int i=0; params[i] != null; i++)
 {
      System.out.print(params[i].getType()+ " " +params[i].getName());
      if(params[i+1] != null)
           System.out.print(", ");
 }

If you have 2 parameters, ie. i goes from 0 to 1, then you will try to access

params[1]
params[2] // out of bounds

This will basically always go out of bounds because you try to access one more than the number of elements in the array.

Here's how you can join elements with , correctly:

Clearest way to comma-delimit a list (Java)?

edited May 23 '17 at 10:32

Community

1
1

answered Jul 02 '14 at 06:00

Sotirios Delimanolis

274,122
60
696
724

Thanks, this way I can use method one to add commas after all but last parameters. – Jack Jul 02 '14 at 06:19

score 1 · Answer 2 · answered Jul 02 '14 at 06:02

1

Ok, the mistake lies in:

for(int i = 0; params[i].....

This throws an exception if params is empty. Example: params has in elements. Trying to get the 0th element will be out on bounds.

To ensure this doesn't happen:

for(int i = 0; i < params.length && params[i]...

answered Jul 02 '14 at 06:02

Dean Leitersdorf

1,303
1
11
22

Thanks. I expected params to be null when there is no parameter to the method. But i was wrong. – Jack Jul 02 '14 at 06:20

score 0 · Answer 3 · answered Jul 02 '14 at 06:02

0

In this line you get an Exception if i is bigger than the last index:

for(int i=0; params[i] != null; i++)

you have to change to:

for(int i=0; i<params.length; i++)

answered Jul 02 '14 at 06:02

Jens

67,715
15
98
113

vinayknl · Answer 4 · 2014-07-02T06:13:10.387

Looks like intention is to loop on the array and append "," except for last entry. Below should work Need to check for boundary condition as well

        for(int i=0; i<params.length; i++)
        {
            if(params[i] != null)
            {
             System.out.print(params[i].getType()+ " " +params[i].getName());

             if(i != params.length-1)
                 System.out.print(", ");
            }
        }

Iterating through Parameter Array - Java Reflection

4 Answers4