Use List instead of ArrayList for the interfaces of the strategy classes.

jplag/src/main/java/de/jplag/strategy/AbstractComparisonStrategy.java

@@ -1,7 +1,7 @@
 package de.jplag.strategy;
 
-import java.util.ArrayList;
 import java.util.Hashtable;
+import java.util.List;
 import java.util.Optional;
 
 import de.jplag.GreedyStringTiling;
@@ -24,7 +24,7 @@ public abstract class AbstractComparisonStrategy implements ComparisonStrategy {
         this.options = options;
     }
 
-    protected void compareSubmissionsToBaseCode(ArrayList<Submission> submissions, Submission baseCodeSubmission) {
+    protected void compareSubmissionsToBaseCode(List<Submission> submissions, Submission baseCodeSubmission) {
         for (Submission currentSubmission : submissions) {
             JPlagComparison baseCodeMatch = greedyStringTiling.compareWithBaseCode(currentSubmission, baseCodeSubmission);
             baseCodeMatches.put(currentSubmission.getName(), baseCodeMatch);

jplag/src/main/java/de/jplag/strategy/ComparisonStrategy.java

@@ -1,6 +1,6 @@
 package de.jplag.strategy;
 
-import java.util.ArrayList;
+import java.util.List;
 
 import de.jplag.JPlagResult;
 import de.jplag.Submission;
@@ -16,5 +16,5 @@ public interface ComparisonStrategy {
      * @param baseCodeSubmission is the base code on which each submission is based on.
      * @return the comparison results.
      */
-    JPlagResult compareSubmissions(ArrayList<Submission> submissions, Submission baseCodeSubmission);
+    JPlagResult compareSubmissions(List<Submission> submissions, Submission baseCodeSubmission);
 }

jplag/src/main/java/de/jplag/strategy/NormalComparisonStrategy.java

@@ -16,7 +16,7 @@ public class NormalComparisonStrategy extends AbstractComparisonStrategy {
     }
 
     @Override
-    public JPlagResult compareSubmissions(ArrayList<Submission> submissions, Submission baseCodeSubmission) {
+    public JPlagResult compareSubmissions(List<Submission> submissions, Submission baseCodeSubmission) {
         boolean withBaseCode = baseCodeSubmission != null;
         if (withBaseCode) {
             compareSubmissionsToBaseCode(submissions, baseCodeSubmission);

jplag/src/main/java/de/jplag/strategy/ParallelComparisonStrategy.java

@@ -35,7 +35,7 @@ public class ParallelComparisonStrategy extends AbstractComparisonStrategy {
     }
 
     @Override
-    public JPlagResult compareSubmissions(ArrayList<Submission> submissions, Submission baseCodeSubmission) {
+    public JPlagResult compareSubmissions(List<Submission> submissions, Submission baseCodeSubmission) {
         // Initialize:
         long timeBeforeStartInMillis = System.currentTimeMillis();
         boolean withBaseCode = baseCodeSubmission != null;
@@ -72,7 +72,7 @@ public class ParallelComparisonStrategy extends AbstractComparisonStrategy {
     /**
      * @return a list of all submission tuples to be processed.
      */
-    private List<SubmissionTuple> buildComparisonTuples(ArrayList<Submission> submissions) {
+    private List<SubmissionTuple> buildComparisonTuples(List<Submission> submissions) {
         List<SubmissionTuple> tuples = new ArrayList<>();
         for (int i = 0; i < (submissions.size() - 1); i++) {
             Submission first = submissions.get(i);