Added @NotNull and @Nullable annotations.

Author: koca2000

pom.xml

@@ -21,6 +21,12 @@
             <version>5.8.2</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.jetbrains</groupId>
+            <artifactId>annotations</artifactId>
+            <version>23.0.0</version>
+            <scope>compile</scope>
+        </dependency>
     </dependencies>
 
     <build>

src/main/java/cz/koca2000/nbs4j/CustomInstrument.java

@@ -1,5 +1,8 @@
 package cz.koca2000.nbs4j;
 
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
 public class CustomInstrument {
 
     private String name = "";
@@ -16,7 +19,7 @@ public CustomInstrument(){}
      * Creates a copy of the custom instrument. Copy is not frozen and does not belong to any song.
      * @param customInstrument custom instrument to be copied
      */
-    public CustomInstrument(CustomInstrument customInstrument){
+    public CustomInstrument(@NotNull CustomInstrument customInstrument){
         name = customInstrument.name;
         fileName = customInstrument.fileName;
         key = customInstrument.key;
@@ -26,7 +29,8 @@ public CustomInstrument(CustomInstrument customInstrument){
         song = null;
     }
 
-    CustomInstrument setSong(Song song){
+    @NotNull
+    CustomInstrument setSong(@NotNull Song song){
         if (this.song != null)
             throw new IllegalStateException("Custom instrument was already added to a song.");
 
@@ -41,11 +45,10 @@ CustomInstrument setSong(Song song){
      * @throws IllegalArgumentException if the argument is null.
      * @throws IllegalStateException if the custom instrument is frozen and can not be modified
      */
-    public CustomInstrument setName(String name){
+    @NotNull
+    public CustomInstrument setName(@NotNull String name){
         throwIfFrozen();
 
-        if (name == null)
-            throw new IllegalArgumentException("Name can not be null");
         this.name = name;
         return this;
     }
@@ -57,11 +60,10 @@ public CustomInstrument setName(String name){
      * @throws IllegalArgumentException if the argument is null.
      * @throws IllegalStateException if the custom instrument is frozen and can not be modified
      */
-    public CustomInstrument setFileName(String fileName){
+    @NotNull
+    public CustomInstrument setFileName(@NotNull String fileName){
         throwIfFrozen();
 
-        if (fileName == null)
-            throw new IllegalArgumentException("File name can not be null");
         this.fileName = fileName;
         return this;
     }
@@ -73,6 +75,7 @@ public CustomInstrument setFileName(String fileName){
      * @throws IllegalArgumentException if the argument is not in range [0; 87] inclusive.
      * @throws IllegalStateException if the custom instrument is frozen and can not be modified
      */
+    @NotNull
     public CustomInstrument setKey(int key){
         throwIfFrozen();
 
@@ -88,6 +91,7 @@ public CustomInstrument setKey(int key){
      * @return this instance of {@link CustomInstrument}
      * @throws IllegalStateException if the custom instrument is frozen and can not be modified
      */
+    @NotNull
     public CustomInstrument setShouldPressKey(boolean shouldPressKey) {
         throwIfFrozen();
 
@@ -99,6 +103,7 @@ public CustomInstrument setShouldPressKey(boolean shouldPressKey) {
      * Returns the name of this custom instrument.
      * @return name of the instrument
      */
+    @NotNull
     public String getName() {
         return name;
     }
@@ -107,6 +112,7 @@ public String getName() {
      * Returns name of the file used in OpenNoteBlockStudio for this custom instrument.
      * @return file name
      */
+    @NotNull
     public String getFileName() {
         return fileName;
     }
@@ -119,6 +125,15 @@ public int getKey() {
         return key;
     }
 
+    /**
+     * Returns the song this custom instrument belongs to.
+     * @return {@link Song} if the custom instrument was added to a song; otherwise, null
+     */
+    @Nullable
+    public Song getSong() {
+        return song;
+    }
+
     /**
      * Returns whether OpenNoteBlockStudio should press key on piano when playing this instrument's note.
      * @return true if the key should be pressed; otherwise, false

src/main/java/cz/koca2000/nbs4j/Layer.java

@@ -1,5 +1,8 @@
 package cz.koca2000.nbs4j;
 
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -25,7 +28,7 @@ public Layer(){}
      * Makes a copy of the layer and its notes. Copy is not frozen.
      * @param layer layer to be copied
      */
-    public Layer(Layer layer){
+    public Layer(@NotNull Layer layer){
         name = layer.name;
         volume = layer.volume;
         panning = layer.panning;
@@ -39,7 +42,8 @@ public Layer(Layer layer){
         }
     }
 
-    Layer setSong(Song song){
+    @NotNull
+    Layer setSong(@NotNull Song song){
         if (this.song != null)
             throw new IllegalStateException("Layer was already added to a song.");
 
@@ -58,7 +62,7 @@ void removedFromSong(){
         this.song = null;
     }
 
-    void setNoteInternal(int tick, Note note, boolean fromSong){
+    void setNoteInternal(int tick, @NotNull Note note, boolean fromSong){
         if (!fromSong && song != null) {
             song.setNote(tick, getIndexInSong(), note);
             return;
@@ -71,7 +75,8 @@ void setNoteInternal(int tick, Note note, boolean fromSong){
         notes.put(tick, note);
     }
 
-    public Layer setNote(int tick, Note note){
+    @NotNull
+    public Layer setNote(int tick, @NotNull Note note){
         setNoteInternal(tick, note, false);
         return this;
     }
@@ -88,6 +93,7 @@ void removeNoteInternal(int tick, boolean fromSong){
         }
     }
 
+    @NotNull
     public Layer removeNote(int tick){
         removeNoteInternal(tick, false);
         return this;
@@ -110,6 +116,7 @@ void freeze(){
      * @return this instance of {@link Layer}
      * @throws IllegalStateException if the layer is frozen and can not be modified
      */
+    @NotNull
     public Layer setLocked(boolean locked){
         throwIfFrozen();
 
@@ -123,7 +130,8 @@ public Layer setLocked(boolean locked){
      * @return this instance of {@link Layer}
      * @throws IllegalStateException if the layer is frozen and can not be modified
      */
-    public Layer setName(String name){
+    @NotNull
+    public Layer setName(@NotNull String name){
         throwIfFrozen();
 
         this.name = name;
@@ -137,6 +145,7 @@ public Layer setName(String name){
      * @throws IllegalArgumentException if the panning is out of range [-100; 100] inclusive]
      * @throws IllegalStateException if the layer is frozen and can not be modified
      */
+    @NotNull
     public Layer setPanning(int panning){
         throwIfFrozen();
 
@@ -158,6 +167,7 @@ public Layer setPanning(int panning){
      * @throws IllegalArgumentException if volume is outside of range [0; 100] inclusive.
      * @throws IllegalStateException if the layer is frozen and can not be modified
      */
+    @NotNull
     public Layer setVolume(int volume){
         throwIfFrozen();
 
@@ -188,6 +198,7 @@ public int getVolume(){
      * Returns the display name of the layer
      * @return name of the layer
      */
+    @NotNull
     public String getName() {
         return name;
     }
@@ -221,6 +232,7 @@ public boolean isFrozen(){
      * @param tick tick of the note
      * @return {@link Note} if there is a note on the give tick; otherwise, null
      */
+    @Nullable
     public Note getNote(int tick){
         return notes.getOrDefault(tick, null);
     }
@@ -229,6 +241,7 @@ public Note getNote(int tick){
      * Returns unmodifiable {@link Map} of notes indexed by their tick.
      * @return unmodifiable {@link Map}
      */
+    @NotNull
     public Map<Integer, Note> getNotes(){
         return Collections.unmodifiableMap(notes);
     }
@@ -252,6 +265,7 @@ public int getIndexInSong(){
      * Returns the song this layer belongs to.
      * @return {@link Song} if the layer was added to a song; otherwise, null
      */
+    @Nullable
     public Song getSong() {
         return song;
     }

src/main/java/cz/koca2000/nbs4j/NBSReader.java

@@ -1,5 +1,7 @@
 package cz.koca2000.nbs4j;
 
+import org.jetbrains.annotations.NotNull;
+
 import java.io.BufferedInputStream;
 import java.io.DataInputStream;
 import java.io.IOException;
@@ -9,7 +11,8 @@ class NBSReader {
 
     private NBSReader(){}
 
-    public static Song readSong(InputStream stream) {
+    @NotNull
+    public static Song readSong(@NotNull InputStream stream) {
         Song song = new Song();
 
         try {
@@ -32,21 +35,22 @@ public static Song readSong(InputStream stream) {
         return song;
     }
 
-    private static short readShort(DataInputStream dataInputStream) throws IOException {
+    private static short readShort(@NotNull DataInputStream dataInputStream) throws IOException {
         int byte1 = dataInputStream.readUnsignedByte();
         int byte2 = dataInputStream.readUnsignedByte();
         return (short) (byte1 + (byte2 << 8));
     }
 
-    private static int readInt(DataInputStream dataInputStream) throws IOException {
+    private static int readInt(@NotNull DataInputStream dataInputStream) throws IOException {
         int byte1 = dataInputStream.readUnsignedByte();
         int byte2 = dataInputStream.readUnsignedByte();
         int byte3 = dataInputStream.readUnsignedByte();
         int byte4 = dataInputStream.readUnsignedByte();
         return (byte1 + (byte2 << 8) + (byte3 << 16) + (byte4 << 24));
     }
 
-    private static String readString(DataInputStream dataInputStream) throws IOException {
+    @NotNull
+    private static String readString(@NotNull DataInputStream dataInputStream) throws IOException {
         int length = readInt(dataInputStream);
         StringBuilder builder = new StringBuilder(length);
         for (; length > 0; --length) {
@@ -59,7 +63,8 @@ private static String readString(DataInputStream dataInputStream) throws IOExcep
         return builder.toString();
     }
 
-    private static HeaderData readHeader(Song song, DataInputStream stream) throws IOException {
+    @NotNull
+    private static HeaderData readHeader(@NotNull Song song, @NotNull DataInputStream stream) throws IOException {
         HeaderData data = new HeaderData();
 
         short length = readShort(stream);
@@ -76,7 +81,7 @@ private static HeaderData readHeader(Song song, DataInputStream stream) throws I
         return data;
     }
 
-    private static void readMetadata(Song song, HeaderData header, DataInputStream stream) throws IOException {
+    private static void readMetadata(@NotNull Song song, @NotNull HeaderData header, @NotNull DataInputStream stream) throws IOException {
         SongMetadata metadata = song.getMetadata();
 
         metadata.setTitle(readString(stream))
@@ -100,7 +105,7 @@ private static void readMetadata(Song song, HeaderData header, DataInputStream s
         }
     }
 
-    private static void readNotes(Song song, HeaderData header, DataInputStream stream) throws IOException {
+    private static void readNotes(@NotNull Song song, @NotNull HeaderData header, @NotNull DataInputStream stream) throws IOException {
         short tick = -1;
         while (true) {
             short jumpTicks = readShort(stream); // jumps till next tick
@@ -137,7 +142,7 @@ private static void readNotes(Song song, HeaderData header, DataInputStream stre
         }
     }
 
-    private static void readLayers(Song song, HeaderData header, DataInputStream stream) throws IOException {
+    private static void readLayers(@NotNull Song song, @NotNull HeaderData header, @NotNull DataInputStream stream) throws IOException {
         for (int i = 0; i < song.getLayersCount(); i++) {
             Layer layer = song.getLayer(i);
 
@@ -153,7 +158,7 @@ private static void readLayers(Song song, HeaderData header, DataInputStream str
         }
     }
 
-    private static void readCustomInstruments(Song song, DataInputStream stream) throws IOException {
+    private static void readCustomInstruments(@NotNull Song song, @NotNull DataInputStream stream) throws IOException {
         byte customInstrumentCount = stream.readByte();
 
         for (int index = 0; index < customInstrumentCount; index++) {