"if" or "where" in for loop of arraylist in java?

Question

I'm sorry if the question is a bit vague so i'll try to explain it.

I got this code:

    public String toString()
{
    String s = "text.\n";

    for (Klus k : alleKlussen)
    {
        s += k.toString() + ".\n";
    }
    return s;
}

But I want to make different loops for different conditions. For example, "Klus" has a couple of variables like: status, date etc.

I'm not very experienced with java yet, but would it be possible to do something like this:

for (Klus k : alleKlussen; status = "completed")
{..}

I know this is wrong but I'd like it to show all "Klus" objects where the status is "completed" and all "Klus" objects where the statis is "not completed".

Thanks and if anything is unclear or I used the wrong word for something, please tell me.

Edit:

It should make something like this:

if (k.getStatus().equals("completed"){
  String s = "completed ones \n"
  s += k.toString() + ".\n"; //get all completed ones
}
if (k.getStatus().equals("uncompleted"){
      String s = "uncompleted ones \n"
      s += k.toString() + ".\n"; //get all uncompleted ones
    }

Please use a StringBuilder for iterative String concatenation! So much object burn... — Quetzalcoatl
– Quetzalcoatl, Commented Apr 5, 2013 at 11:04
your edit basically shows the answer. I fail to see the question now. — Joeri Hendrickx
– Joeri Hendrickx, Commented Apr 5, 2013 at 11:16

Andreas Fester · Accepted Answer · 2013-04-05 11:21:13Z

4

Simply add the condition inside the for() loop:

for (Klus k : alleKlussen) {
    if (k.getStatus().equals("completed")) {
        s += k.toString() + ".\n";
    }
}

From the additional information in the question, it seems like the following is what is intended:

String completed = "completed ones \n";
String uncompleted = "uncompleted ones \n";

for (Klus k : alleKlussen) {

    if (k.getStatus().equals("completed")) {
      completed += k.toString() + ".\n"; //get all completed ones
    }
    else if (k.getStatus().equals("uncompleted")) {
       uncompleted += k.toString() + ".\n"; //get all uncompleted ones
    }
}

You should also consider using a StringBuilder to create the result strings, which reduces the memory overhead.

edited Apr 5, 2013 at 11:21

answered Apr 5, 2013 at 11:03

Andreas Fester

36.8k9 gold badges101 silver badges125 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Colinch Over a year ago

Thanks! I forgot about the if statement but it's not exactly what I'm looking for, I think I explained it a bit wrong. I edited my question

Colinch Over a year ago

This works for all completed ones, but how should i do the same for the uncompleted ones? just make another for-loop in the toString()?

Andreas Fester Over a year ago

@colin check my updated answer - is this what you need? You have two different Strings afterwards, containing information from completed and uncompleted objects. You could use two for() loops, but then you would need to iterate your list twice

Simon Hellinger Over a year ago

Depending on what @colin needs, he could always just concatenate the two strings and return the result

Colinch Over a year ago

Thanks, this did it for me. I just needed a list with the completed and uncompleted ones and this does just that!

IndoKnight · Accepted Answer · 2013-04-05 11:18:51Z

2

You can use switch if you have many conditions and it is easy to read

for (Klus k : alleKlussen) {

switch(k.getStatus()){
       case "completed": ....
                          break;

       case "uncompleted": ....
                            break;

        default: ...
}

}

Please note switch with String literals is only supported in Java 7.

edited Apr 5, 2013 at 11:18

answered Apr 5, 2013 at 11:08

IndoKnight

1,8641 gold badge21 silver badges31 bronze badges

6 Comments

Simon Hellinger Over a year ago

Why, this would be a perfect case for enums, even if String literals are supported

Colinch Over a year ago

Thanks for your answer, but how should it select only the "Klus" objects with "completed" in that case?

IndoKnight Over a year ago

@Colin It is not possible to "just" get "Klus" objects depending on object status in this scenario. You need to iterate through the objects and check.

IndoKnight Over a year ago

@Simon I agree, but in the original question the user is not using enums. He is using status as String literals.

Colinch Over a year ago

I think this everntually also would've worked, but the other one was a bit more simple because I haven't learned to use cases yet. Thanks anyway!

|

NPKR · Accepted Answer · 2013-04-05 11:05:07Z

0

   Use this - this toString will print only Klus are completed.
 public String toString()
    {
        String s = "text.\n";

        for (Klus k : alleKlussen)
        {
            if("completed".equals(k.getStatus ()))
            s += k.toString() + ".\n";
        }
        return s;
    }

answered Apr 5, 2013 at 11:05

NPKR

5,5165 gold badges35 silver badges48 bronze badges

Comments

Qwerky · Accepted Answer · 2013-04-05 11:05:26Z

0

Why not just do the standard if-conditionals, such as:

if ("".equals(k.getStatus())) {

} else if ("completed".equals(k.getStatus())) {

}

edited Apr 5, 2013 at 11:05

Qwerky

18.5k6 gold badges48 silver badges85 bronze badges

answered Apr 5, 2013 at 11:04

Grant Thomas

45.1k10 gold badges88 silver badges129 bronze badges

2 Comments

Rahul Over a year ago

A person with 20k rep suggestion to use == for String value comparison? Unbelievable.

Grant Thomas Over a year ago

@R.J That wasn't my suggestion, my suggestion was to use a standard convention in most languages - if statements - the equality check was incidentally my lack of knowledge of Java specifically, but I don't think that detracts from the actual suggestion. Unbelievably judgmental, maybe, as if you expect I got 20k rep in the java.

Simon Hellinger · Accepted Answer · 2013-04-05 11:27:52Z

0

To append the uncompleted after the completed ones, try this (And I suggest using enums, but you are welcome to stick to Strings. But then this will only work in Java SE 7!):

State.java:

// Makes switches easy to use and String typos are impossible
public enum State { COMPLETE, INCOMPLETE };

Replace your current String "state" with the enum like so:

Klus:java

public class Klus {
   private State state;
   ...
   public State getState() { return this.state; }
   ...
}

Now use it in a switch in the for loop. Use two strings, one for complete, one for incomplete. Append them in the end. (Note the use of StringBuilder instead of str +=... )

Class containing your toString():

public String toString() {
    StringBuilder complete = new StringBuilder("completed ones \n"), 
                  uncompleted = new StringBuilder("uncompleted ones \n");
    for(Klus k : alleKlussen) {
       switch(k.getStatus())
       case COMPLETE:
          complete.append(k.toString()).append(".\n"); break;
       case INCOMPLETE:
          uncompleted.append(k.toString()).append(".\n"); break;
       default:
       }
    }

    complete.append(uncompleted.toString();

    return complete.toString();
}

edited Apr 5, 2013 at 11:27

answered Apr 5, 2013 at 11:22

Simon Hellinger

1,33912 silver badges21 bronze badges

2 Comments

Colinch Over a year ago

Thanks for the answer, I see a lot of things I haven't heard about yet. But maybe in the final version I could also use this method for the statuses. Thanks.

Simon Hellinger Over a year ago

@colin you're welcome. Andreas' answer helps you out without all the extra bells and whistles, though :-D Have fun coding!

Collectives™ on Stack Overflow

"if" or "where" in for loop of arraylist in java?

5 Answers 5

5 Comments

6 Comments

Comments

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

5 Comments

6 Comments

Comments

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related