Copy part of another array in Java

Question

I'm new to Java, and I had a quick question.

I have an array named studentInfo[0] that I created from:String studentInfo[] = line.split(","); I would like to make another array from it's first index.

In other words. I have the array studentInfo that lets say looks like this: "a,b,c,d,
a1,b1,c1,d1, a2,b2,d2,c2 etc... " I want another array that takes all the "a" in my other array. Example: "a,a1,a2 etc..."

How would I do this?

I have tried System.arraycopy(studentInfo, 0, array, 0, studentInfo.length); But doesn't seem to work because it does not just give me the first index.

FYI my code is in a while loop which loops every time it hits a new line. See below:

 while ((line = reader.readLine()) != null) {
            String studentInfo[] = line.split(",");
            String array[] = new String[0];
      }

Thank you!

"But it does not seem to work" - What is it doing? What shouls it be doing? "doesnt seem to work" doesnt help us figure out the problem. HOW is it not working? "FYI my code is in a while loop which loops every time it hits a new line." - You should probably show this code — Vince
– Vince, Commented Nov 17, 2014 at 18:31

Ringo · Accepted Answer · 2014-11-17 18:42:35Z

1

I would do something like.

String[] studentInfoA = new String[50] //You can put the size you want.

    for(int i=0; i<studentInfo.length-1; i++){
        if(studentInfo[i].substring(0,1).equals("a")){
           studentInfoA[i]=studentInfo[i];
        }
    }

i would recommend Vimsha's answer better but since you are learning i didnt want to make you struggle with collections and such, or at least i wouldnt like you to use them without properly knowing about arrays and loops.

answered Nov 17, 2014 at 18:42

Ringo

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usha · Accepted Answer · 2014-11-17 18:39:51Z

Assuming you have this array,

studentInfo = ["a","b","c","d","a1","b1","c1","d1", "a2","b2","d2","c2"]

and you want another array like

studentInfoWithA = ["a", "a1", "a2"]

then

    String studentInfo[] = new String[] { "a", "b", "c", "d", "a1", "b1", "c1", "d1", "a2", "b2", "d2", "c2" };

    List<String> newList = new ArrayList<String>();
    for (String info : studentInfo) {
        if (info.startsWith("a")) {
            newList.add(info);
        }
    }

    String[] studentInfoWithA = newList.toArray(new String[0]);

vrudkovsk · Accepted Answer · 2014-11-17 19:01:45Z

0

In java 1.8, filtering looks like

String[] result = Arrays.stream(new String[] { "a","b","c","d","a1","b1","c1","d1", "a2","b2","d2","c2" })
    .filter(e -> e.startsWith("a"))
    .toArray(String[]::new);

answered Nov 17, 2014 at 19:01

vrudkovsk

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