Build all possible phrase pairs from a sentence pair I have an array for an English sentence (enSentence) and for a German sentence (deSentence). Each value represents one word. I want to print every possible phrase pair (enPhrase and dePhrase), where no phrase contains more than maxhPhraseLength words. A phrase can consist of a single word, all words of the sentence, and everything inbetween (consecutive).

So for Hello world ! and Hallo Welt !, possible phrase pairs would be:


Hello - Hallo
Hello world - Hallo
Hello world ! - Hallo
world - Hallo
world ! - Hallo
! - Hallo
…
Hello - Hallo Welt
Hello - Hallo Welt !
Hello - Welt
…
Hello world ! - Hallo Welt !


But phrases like Hello ! or world Hello are not possible.

This is my first try:

enLoop:
for(int en1 = 0; en1 &lt; enSentence.length; en1++) {
  for(int en2 = en1; en2 &lt; enSentence.length; en2++) {

    if(en2-en1+1 &gt; maxPhraseLength) {
      continue enLoop;
    }

    deLoop:
    for(int de1 = 0; de1 &lt; deSentence.length; de1++) {
       for(int de2 = de1; de2 &lt; deSentence.length; de2++) {

         if(de2-de1+1 &gt; maxPhraseLength) {
           continue deLoop;
         }

         // building the phrase pair
         enPhrase = "";
         dePhrase = "";
         for(int e = en1; e &lt;= en2; e++) {
           enPhrase = enPhrase + " " + enSentence[e];
         }
         for(int d = de1; d &lt;= de2; d++) {
           dePhrase = dePhrase + " " + deSentence[d];
         }
         enPhrase = enPhrase.trim();
         dePhrase = dePhrase.trim();
         System.out.println(enPhrase + " - " + dePhrase);

       }
     }

  }
}


I’m interested in any kind of feedback (I rarely create code from scratch).

I considered naming the variables language-neutral (in case I want to use the code for making phrase pairs in other languages, too), but couldn’t come up with something short and catchy (sourceSentence/source1 and targetSentence/target1 are longer, and I always have to remind myself what the source and what the target is, while it’s immediately clear to me if thinking about the terms en/English and de/German instead; but the difference doesn’t really matter in this case anyway).
Repeating work

You should move all of the code that computes enPhrase to before the deLoop.  There is no need to recompute enPhrase each time you modify de2.

Furthermore, when you compute dePhrase, you can do so by appending the next word deSentence[de2] to the current dePhrase.  Right now you reconstruct all of dePhrase in the inner loop, making it an \$O(n)\$ operation when it could be an \$O(1)\$ operation.

Get rid of loop labels

You can get rid of the loop labels if you precalculate the proper end of the loop.

Use StringBuilder

It's more efficient to use a StringBuilder to concatenate strings rather than using the + operator.

Rewrite

Here is a rewrite showing the above changes:

StringBuilder enPhrase = new StringBuilder();
StringBuilder dePhrase = new StringBuilder();

for(int en1 = 0; en1 &lt; enSentence.length; en1++) {
  int en2Max = Math.min(enSentence.length, en1+maxPhraseLength);
  for(int en2 = en1; en2 &lt; en2Max; en2++) {
    if (en2 == en1) {
      enPhrase.setLength(0);
    } else {
      enPhrase.append(" ");
    }
    enPhrase.append(enSentence[en2]);
    for(int de1 = 0; de1 &lt; deSentence.length; de1++) {
       int de2Max = Math.min(deSentence.length, de1+maxPhraseLength);
       for(int de2 = de1; de2 &lt; de2Max; de2++) {
         if (de2 == de1) {
           dePhrase.setLength(0);
         } else {
           dePhrase.append(" ");
         }
         dePhrase.append(deSentence[de2]);

         System.out.print(enPhrase.toString());
         System.out.print(" - ");
         System.out.println(dePhrase.toString());
       }
     }

  }
}