CODEWITHSUNDEEP
javastring
jason
jason

Reputation: 7164

How to create a string from many strings efficiently in Java

In a Java code, I have 11 different strings, some of them (at most 9) can be null. Strings are a part of an object. If none of them is null, I make a string like this : 

string1 + "," + string2 + "," + string3 + "," + string4 + "," + string5 + "," + string6 + "(" + string7 + ")" + string8 + string9 + "+" + string10 + string11

If none of them is null, it's okey. But some of them can be null. If I check if each of them is null, code gets really slow and long. How can I generate such a string in an efficient and fast way? Thanks.

Upvotes: 1

Views: 265

Answers (5)

ccc
ccc

Reputation: 370

If 6th index of your string is always surrounded by ( and ) then you can use following code.

    List<String> vals = new ArrayList<>();
    vals.add(string1);
    vals.add(string2);
    vals.add(string3);
    vals.add(string4);
    vals.add(string5);
    vals.add(string6);
    vals.add(string7);
    vals.add(string8);
    vals.add(string9);
    vals.add(string10);
    vals.add(string11);

    for (int i =0 ; i < vals.size(); i++) {
        // check null values
        if (vals.get(i) != null) {
        // as your requirement surround 7th value with ( and )
            if(vals.indexOf(vals.get(i)) == 6) {
                values += "\b(" + vals.get(i)+")";
            } else {
                values += vals.get(i)+",";
            }
        }
    }
    System.out.println(values+"\b");

Output if 4th and 9th strings are null then,

test1,test2,test3,test5,test6(test7)test8,test10,test11

Upvotes: 1

Bon
Bon

Reputation: 3103

If you simply want your code to be as short as possible, use String.format and get rid of the "null" in the string.

String result = String.format("%s,%s,%s,%s,%s,%s(%s)%s,%s,%s,%s",
            string1, string2, string3, string4, string5,
            string6, string7, string8, string9, string10,
            string11);

    System.out.println(result.replace("null", ""));

Upvotes: 1

CMR
CMR

Reputation: 985

In Java 8, you can stream and join with Collectors, and filter with Objects classes

List<String> strings = Arrays.asList("first", "second", null, "third", null, null, "fourth");
String res = strings.stream().filter(Objects::nonNull).collect(Collectors.joining(","));
System.out.println(res);

results in output

first,second,third,fourth

Upvotes: 1

Marko Topolnik
Marko Topolnik

Reputation: 200226

With Java 8 you could use this for the first part with comma-delimited strings:

String part1 = Stream.of(string1, string2, string3, string4, string5, string6)
                     .filter(Objects.notNull())
                     .collect(joining(",");

From then on you have an irregular structure so you'll need custom logic to handle it. The helper function

static String emptyForNull(String s) {
  return s == null ? "" : s;
}

can get you part of the way.

Upvotes: 2

i23
i23

Reputation: 496

public static void main(String[] args) {
    String string1 = "test1";
    String string2 = "test2";
    String string3 = "test3";
    String string4 = null;
    String string5 = "test5";

    StringBuilder stringBuilder = new StringBuilder();

    List<String> valueList = new ArrayList<>();
    valueList.add(string1);
    valueList.add(string2);
    valueList.add(string3);
    valueList.add(string4);
    valueList.add(string5);
    // etc.

    for (String value : valueList) {
        if (value != null) {
            stringBuilder.append(value);
        }
        else {
            value = ",";
            stringBuilder.append(value);
        }
    }
    System.out.println(stringBuilder);
}

Output :

test1test2test3,test5

Upvotes: 3

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