Java/kotlin format string that read from file using array

Question

As title says, I want to know is there any convent way to format string using array in Java.

Let me hold an kotlin example.

var sentences = arrayOf("hello", "world")
var template = "Dialogue: ${sentences[0]}\n" +
                "Dialogue: ${sentences[1]}\n"

template.format(sentences)

print(template)

Above code works well. So how about Java ?

EDIT

I am sorry I have not described my question clearly. And when I run into my real case I found my code cannot work for me now.

In fact, template is read from a file.

var sentences = arrayOf("hello", "world")
var template = File("template.txt").readText()

template.format(sentences)
print(template)

And template.txt file contains:

Dialogue: ${sentences[0]}
Dialogue: ${sentences[1]}

As you see, I want to read file then format the result.

In addition, I am so sorry about this question. Because it seems to be changed to how to format string which is read from file.

According to your edit, it becomes an extremely complicated question.. — ice1000
– ice1000, Commented Apr 27, 2018 at 5:29

ice1000 · Accepted Answer · 2018-04-27 03:52:04Z

4

The code above is completely wrong use of String.format. Let me explain why.

In the first two line:

var sentences = arrayOf("hello", "world")
var template = "Dialogue: ${sentences[0]}\n" +
              "Dialogue: ${sentences[1]}\n"

Here, template is already there, it's a String, its value is "Dialogue: hello\nDialogue: world", which is the result you see.

If you don't trust me, try replace sentences with a non-exist variable name. You'll get a compile error, because the string is connected exactly when you create it. "String template" is just a syntax sugar of +.

Then, you've invoked template.format, which is actually String.format, the returned string is not used.

Since this is already wrong in Kotlin, you can do the same thing in Java easily:

String[] sentences = new String { "hello", "world" };
String template = "Dialogue: " + sentences[0] + "\n" +
                  "Dialogue: " + sentences[1] + "\n";

template.format(sentences);

System.out.print(template);

This code equals to the Kotlin code you've given.

I guess you want this:

String template = String.format("Dialogue: %s%nDialogue: %s%n", sentences);
System.out.print(template);

edited Apr 27, 2018 at 3:52

answered Apr 27, 2018 at 3:35

ice1000

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5 Comments

Jonathan Lam Over a year ago

Is this an answer? (it's also a bit rude)

ice1000 Over a year ago

I've posted the answer. @JonathanLam

Jonathan Lam Over a year ago

I don't see how this is any different from my answer.

ice1000 Over a year ago

I've given an ideal approach (same as you) and the approach same to his example (you don't have)

CoXier Over a year ago

You are right. But I will tell you why I should do this.

Jonathan Lam · Accepted Answer · 2018-04-27 03:34:23Z

2

You can use String.format():

String[] sentences = { "hello", "world" };
String template = "Dialogue: %s%nDialogue: %s%n";
String result = String.format(template, arr[0], arr[1]);

edited Apr 27, 2018 at 3:34

answered Apr 27, 2018 at 3:32

Jonathan Lam

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7 Comments

Phil Over a year ago

OPs example with the array is more akin to MessageFormat

Jonathan Lam Over a year ago

@Phil I was not aware of that class. I'll leave this answer up if it helps anyone though.

Rag Over a year ago

In my opinion this would be easier to read with straight string concatenation rather than relying on format strings. The compiler will optimize it automatically with a StringBuilder.

Jonathan Lam Over a year ago

@BrianGordon That's also very interesting. I'm not too familiar with Java and I guess I need to learn about these utility classes (i.e., MessageFormat and StringBuilder

ice1000 Over a year ago

He did use it, template.format is the same as String.format.

|

Muli Yulzary · Accepted Answer · 2022-01-02 11:55:10Z

0

Use %s for substitutions in the template file. Kotlin (Java) will then call the toString method for each argument and replace them with respect to the order of the arguments.

//template.txt
%s magnificent %s!

//Main.kt
val sentences = arrayOf("hello", "world")
val template = File("template.txt").readText()

template.format(sentences) // hello magnificent world!

edited Jan 2, 2022 at 11:55

answered May 1, 2018 at 13:59

Muli Yulzary

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