仅打印ArrayList中元素的设置值？

Question

I just want to know how to print out Strings in an ArrayList with a given certain value only for the output. For example: I input "Hot", "Cold", "Pressure", "Pain". What method/control statement should I use to make so that the output will only be the words with four letters?

Output: "Cold" "Pain"

It only prints "Cold" & "Pain" because they're the only one with four elements. Will the use of .set be useful?

Answer 1

• You can add Strings to a map. The key can be the length of the string and the value a list of strings.

Map<Integer, List<String>> -> Map<string length, List<String>>

This one is expected O(1) runtime

• You can keep the strings in a list and traverse them:

List list = ...

    for (String s: list){
        if (s.length()==4){
              print(s);
        }
    }

This one has linear runtime

Answer 2

As explained in the comments, you could iterate over the list. If this is a repeated operation, you could use a map to sort the strings by length. See below an example with the 2 solutions:

public static void main(String[] args) {
    List<String> list = Arrays.asList("Hot", "Cold", "Pressure", "Pain");

    //Solution 1
    for (String s : list) {
        if (s.length() == 4) {
            System.out.println(s); //prints Cold and Pain
        }
    }

    //Solution 2
    Map<Integer, List<String>> map = new HashMap<Integer, List<String>> ();
    for (String s : list) {
        int length = s.length();
        if (map.containsKey(length)) {
            map.get(length).add(s);
        } else {
            map.put(length, new ArrayList<String>(Arrays.asList(s)));
        }
    }

    System.out.println(map.get(4)); //prints [Cold, Pain]
    System.out.println(map.get(3)); //prints [Hot]
}

Answer 3

I'd also check for nulls (don't know if they could occur in your situation) to avoid a possible java.lang.NullPointerException:

    List<String> list = Arrays.asList("Hot", "Cold", "Pressure", null, "Pain");

    for (String s : list) {
        if (s != null && s.length() == 4) {
            System.out.println(s); // prints "Cold" and "Pain"
        }
    }