Filtering strings from an array

Question

I am trying to filter strings from an array. For example I have five strings

adcfd
adjnrj
amlkc
nfldkm
cslkls

If I want to create a new array that contains the filtered array, e.g. it starts with 'ad' it will create an array with two elements [adcfd, adjnrj]

or if it starts with 'a' we will get an array with three elements [adcfd, adjnrj, amlkc]

The only thing in my mind is to compare each character from all the strings until we get two 'trues' then we can end the loop.

If there is any function that I don't know, can I give any suggestions?

Might want to look into regular expressions (regex) if you plan on creating a filter system. — Vince
– Vince, Commented Dec 14, 2016 at 3:09
Take a look at docs.oracle.com/javase/8/docs/api/java/lang/String.html and see if you find some way to determine if a string starts with another string. — Misha
– Misha, Commented Dec 14, 2016 at 3:10
@user306856 Do you know you can accept solution which you think it helps you by checking the tick beside it?? — user3437460
– user3437460, Commented Dec 14, 2016 at 3:23

Noel · Accepted Answer · 2016-12-14 03:22:52Z

2

There is an easier way in Java 8.

Since Stream API is now available to Java.

public static void main(String[] args)
{
   String[] stringArray = {"adcfd", "adjnrj", "amlkc", "nfldkm", "cslkls"};
   List<String> myList = Arrays.asList(stringArray);
   Object[] result = myList.stream().filter(s -> s.startsWith("ad")).toArray();
   for(Object obj : result){
      System.out.println(obj);
   }
 }

Note this will work only in Java 8.

answered Dec 14, 2016 at 3:22

Noel

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choasia · Accepted Answer · 2016-12-14 03:32:38Z

1

    String[] strings = {"adcfd", "adjnrj", "amlkc", "nfldkm", "cslkls"};
    String prefix = "ad";
    String[] result = null;

    // Use String#startsWith
    result = Stream.of(strings).filter(str -> str.startsWith(prefix))
            .collect(Collectors.toSet()).toArray(new String[0]);
    Stream.of(result).forEach(System.out::println); //-> adjnrj adcfd

    // Use String#matches (with regexp)
    result = Stream.of(strings).filter(str -> str.matches("^" + prefix + ".*$"))
            .collect(Collectors.toSet()).toArray(new String[0]);
    Stream.of(result).forEach(System.out::println);  //-> adjnrj adcfd

answered Dec 14, 2016 at 3:32

choasia

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2 Comments

xiaofeng.li Over a year ago

Why do you use toSet() instead of toList()?

choasia Over a year ago

@LukeLee I didn't consider much, just tried to remove duplicated items. toList is also fine if no need to do so.

Wasi Ahmad · Accepted Answer · 2016-12-14 04:03:16Z

You need to use the startsWith method of String class in java. For example,

public static void main(String args[]) {
    String Str = new String("Welcome to StackOverflow");

    System.out.print("Return Value :" );
    System.out.println(Str.startsWith("Welcome") );

    System.out.print("Return Value :" );
    System.out.println(Str.startsWith("StackOverflow") );
}

It prints:

Return Value :true
Return Value :false

Edit: Previously i didn't give straightforward answer to OP's question as i thought OP will try from my given example. Since others have already shared their answer, i am sharing a simple code snippet that will provide OP the desired output.

String[] strings = {"adcfd", "adjnrj", "amlkc", "nfldkm", "cslkls"};
String prefix = "ad";
ArrayList<String> result = new ArrayList<>();
for (String str : strings) {
    if (str.startsWith(prefix)) {
        result.add(str);
    }
}
System.out.println(result.toString());

It prints:

[adcfd, adjnrj]

nail fei · Accepted Answer · 2016-12-14 03:18:49Z

I think you can sort String first then you can get all matched String without compare all string element.

an alternative code segment:

public class Demo {
public List<String> test(String[] strs,String filter){
    List<String> res = new LinkedList<>();
    Arrays.sort(strs);
    for(String str:strs){
        if(str.startsWith(filter)){
            res.add(str);
            continue;
        }
        if(str.compareTo(filter)>0){
            return res;
        }
    }
    return res;
}

 public static void main(String[] args){
    String[] strs = {"adcfd","adjnrj","amlkc","nfldkm","cslkls"};
    Demo demo = new Demo();
    String filter = "a";
    System.out.println(demo.test(strs, filter));
 }
}

output:

[adcfd, adjnrj, amlkc]

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