Use List interface in variable types.

jplag.frontend-utils/src/main/java/de/jplag/TokenHashMap.java

@@ -13,7 +13,7 @@ import java.util.Map;
  * that is larger or equal to the specified size (see {@link TokenHashMap#Table(int)}).
  */
 public class TokenHashMap {
-    private final Map<Integer, ArrayList<Integer>> mappedEntries;
+    private final Map<Integer, List<Integer>> mappedEntries;
     private final int primeNumber;
 
     /**
@@ -50,7 +50,7 @@ public class TokenHashMap {
         if (mappedEntries.containsKey(actualKey)) {
             mappedEntries.get(actualKey).add(value);
         } else {
-            ArrayList<Integer> entries = new ArrayList<>();
+            List<Integer> entries = new ArrayList<>();
             entries.add(value);
             mappedEntries.put(actualKey, entries);
         }

jplag/src/main/java/de/jplag/Submission.java

@@ -13,6 +13,7 @@ import java.nio.file.Path;
 import java.text.DecimalFormat;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.List;
 
 import de.jplag.options.JPlagOptions;
 
@@ -184,7 +185,7 @@ public class Submission implements Comparable<Submission> {
     public String[][] readFiles(String[] files) throws de.jplag.ExitException {
         String[][] result = new String[files.length][];
         String help;
-        ArrayList<String> text = new ArrayList<>();
+        List<String> text = new ArrayList<>();
 
         for (int i = 0; i < files.length; i++) {
             text.clear();

jplag/src/main/java/de/jplag/reporting/Report.java

@@ -332,7 +332,7 @@ public class Report { // Mostly legacy code with some minor improvements.
             String tmp = text[markup.fileIndex][markup.lineIndex];
             // is there any ", &, > or < in the String?
             if (tmp.indexOf('&') >= 0) {
-                ArrayList<String> tmpV = new ArrayList<>();
+                List<String> tmpV = new ArrayList<>();
                 // convert the string into a vector
                 int strLength = tmp.length();
                 for (int k = 0; k < strLength; k++) {