Merging string-Array / arrayList without using loop

Question

I was trying to do something like:

ArrayList<String> getMerged ( String host, String port, String filesToCopy ){
  ArrayList<String> merged = new ArrayList<String>();
  merged.add(host);
  merged.add(port);
  merged.addAll(filesToCopy.split(","));   //which is invalid
  return merged;
}

I want to know if we can add elements of filesToCopy.split(",") with out having the overhead of using a loop.

Also, if the above operation can be done in a string array, say String[] merged (can pass filesToCopy also as String[] if needed), it would be even better coz in the end, I'll be converting this arrayList into an array.

I'm novice in Java programming, so please don't mind if this is a silly question.

Slightly confused. filesToCopy is a list, why would you need to split the strings up within it? Unless filesToCopy is meant to be a single string containing comma delimited file names? Maybe you should look into varargs arguments for methods.... — Dan Temple
– Dan Temple, Commented Mar 26, 2014 at 13:13
I'm also not sure what you are wanting to do with the split. filesToCopy is an ArrayList so what is that supposed to hypothetically accomplish? Show us what you are trying to do using the loop that you don't want to use. — Radiodef
– Radiodef, Commented Mar 26, 2014 at 13:36
@DanTemple & Radiodef - I'm sorry, that was a typo; filesToCopy is a string. "(can pass filesToCopy also as String[] if needed)" - coz I can pass the arg as from caller as filesToCopy.split(","). — human
– human, Commented Mar 27, 2014 at 7:30
Well, for how you have the code now (provide filesToCopy as a String) you can just put Arrays.asList(filesToCopy.split(","); into the addAll() method and it should work fine. — Dan Temple
– Dan Temple, Commented Mar 27, 2014 at 7:40
@Vnm i am not about sure what you trying to do.did you checked my answer.update the status if none of my methods are usefull... — Prakash
– Prakash, Commented Mar 27, 2014 at 7:41

tckmn · Accepted Answer · 2014-03-26 13:11:24Z

1

You could do this in a single array:

String[] files = filesToCopy.split(","); // filesToCopy is an ArrayList, so I'm not
                                         // sure how this works; I'm assuming it's
                                         // a typo. Just get the files array somehow
String[] merged = new String[2 + files.length];
merged[0] = host;
merged[1] = port;
for (int i = 2; i < merged.length; i++) {
    merged[i] = files[i-2];
}

Or, without "the overhead of a loop":

merged[0] = host;
merged[1] = port;
System.arraycopy(files, 0, merged, 2, files.length);

Of course, this still uses a loop "behind the scenes," which is unavoidable.

answered Mar 26, 2014 at 13:11

tckmn

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2 Comments

human Over a year ago

Yeah, that I understand, but I was wondering if it works better than using loop by ourselves. Like mem copy or sys::copy in C

human Over a year ago

I got my answer for performance part from the link: stackoverflow.com/questions/8526907/…

Pablo Lozano · Accepted Answer · 2014-03-26 13:19:17Z

1

ArrayList.addAll method requires a Collection as a parameter, so just pass the filesToCopy:

String [] getMerged ( String host, String port, ArrayList<String> filesToCopy ){
  ArrayList<String> merged = new ArrayList<String>();
  merged.add(host);
  merged.add(port);
  merged.addAll(filesToCopy); 
  return merged.toArray(new String[merged.size());
}

PS: I just a matter of opinion, but if I can choose between arrays and Collections, I always prefer to work with Collections (List, Set). Variable size and easy insertions are things to take into account.

edited Mar 26, 2014 at 13:19

answered Mar 26, 2014 at 13:13

Pablo Lozano

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Comments

Prakash · Accepted Answer · 2014-03-27 11:00:07Z

1

I am not sure about what your need is.But i am sure anyone of the below methods will surely help you..

1.Covert String With Comma To A ArrayList

Program:

    import java.util.Arrays;
    ....  
    String name="java,php,c";
    List<String> list=Arrays.asList(name.split(","));
    System.out.println(" "+list);

OutPut:

    [java, php, c]

2.Covert ArrayList To StringArray

Here we can convert the same arraylist that we got in 1st method to string array.

Program:

    String []names=list.toArray(new String[list.size()]);
    for(String s:names){
            System.out.println(""+s);
    }

OutPut:

    java
    php
    c

3.Covert ArrayList To Comma Seperated String

Here we can convert the same arraylist that we got in 1st method to string array.

For this you need To add commons-lang3-3.2.1.jar into your classpath or project libarary.

You can Download The commons-lang3-3.2.1.jar (HERE)

Program:

    import org.apache.commons.lang3.StringUtils;
    .....
    String name=StringUtils.join(list, ",");
    System.out.println("name="+name);

OutPut:

    name=java,php,c

4.Updated Program

This might me the method that you needed

public String[] getMerged(String host, String port, String filesToCopy) {
    String files[] = filesToCopy.split(",");
    String[] merged = new String[(2 + files.length)];
    merged[0] = host;
    merged[1] = port;
    System.arraycopy(files, 0, merged, 2, files.length);
    return merged;
}

Check out these methods and notify me if your need is something other than these methods..

edited Mar 27, 2014 at 11:00

answered Mar 27, 2014 at 5:21

Prakash

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1 Comment

human Over a year ago

Hi Prakash, to the merged array, I need to two Strings (say host n port) first and then merge the contents of .split(",") to it. If split() was unnecessary, I could've used the method "Pablo Lozano" mentioned, which I knew already..

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