Added CustomBlock#getCustomBlockId, it is now defined by the developer and not increased automatically by a counter

src/main/java/fr/themode/demo/blocks/StoneBlock.java

@@ -37,4 +37,9 @@ public class StoneBlock extends CustomBlock {
     public int getBreakDelay(Player player) {
         return 750;
     }
+
+    @Override
+    public short getCustomBlockId() {
+        return 2;
+    }
 }

src/main/java/fr/themode/demo/blocks/UpdatableBlockDemo.java

@@ -45,4 +45,9 @@ public class UpdatableBlockDemo extends CustomBlock {
     public int getBreakDelay(Player player) {
         return 500;
     }
+
+    @Override
+    public short getCustomBlockId() {
+        return 1;
+    }
 }

src/main/java/net/minestom/server/instance/BlockModifier.java

@@ -47,7 +47,7 @@ public interface BlockModifier {
 
     default void setCustomBlock(int x, int y, int z, String customBlockId, Data data) {
         CustomBlock customBlock = BLOCK_MANAGER.getCustomBlock(customBlockId);
-        setCustomBlock(x, y, z, customBlock.getId(), data);
+        setCustomBlock(x, y, z, customBlock.getCustomBlockId(), data);
     }
 
     default void setCustomBlock(int x, int y, int z, String customBlockId) {

src/main/java/net/minestom/server/instance/Chunk.java

@@ -80,7 +80,7 @@ public class Chunk implements Viewable {
 
     private void setCustomBlock(int x, int y, int z, CustomBlock customBlock, Data data) {
         UpdateConsumer updateConsumer = customBlock.hasUpdate() ? customBlock::update : null;
-        setBlock(x, y, z, customBlock.getBlockId(), customBlock.getId(), data, updateConsumer);
+        setBlock(x, y, z, customBlock.getBlockId(), customBlock.getCustomBlockId(), data, updateConsumer);
     }
 
     private void setBlock(int x, int y, int z, short blockId, short customId, Data data, UpdateConsumer updateConsumer) {
@@ -183,7 +183,7 @@ public class Chunk implements Viewable {
 
     protected void refreshBlockValue(int x, int y, int z, short blockId) {
         CustomBlock customBlock = getCustomBlock(x, y, z);
-        short customBlockId = customBlock == null ? 0 : customBlock.getId();
+        short customBlockId = customBlock == null ? 0 : customBlock.getCustomBlockId();
         refreshBlockValue(x, y, z, blockId, customBlockId);
     }
 

src/main/java/net/minestom/server/instance/block/BlockManager.java

@@ -16,7 +16,7 @@ public class BlockManager {
 
     public void registerCustomBlock(CustomBlock customBlock) {
         String identifier = customBlock.getIdentifier();
-        short id = customBlock.getId();
+        short id = customBlock.getCustomBlockId();
         this.customBlocksInternalId.put(id, customBlock);
         this.customBlocksId.put(identifier, customBlock);
     }

src/main/java/net/minestom/server/instance/block/CustomBlock.java

@@ -6,24 +6,18 @@ import net.minestom.server.instance.Instance;
 import net.minestom.server.utils.BlockPosition;
 import net.minestom.server.utils.time.UpdateOption;
 
-import java.util.concurrent.atomic.AtomicInteger;
-
 /**
  * TODO
  * - option to set the global as "global breaking" meaning that multiple players mining the same block will break it faster (cumulation)
  */
 public abstract class CustomBlock {
 
-    private static final AtomicInteger idCounter = new AtomicInteger();
-
     private short blockId;
     private String identifier;
-    private short id;
 
     public CustomBlock(short blockId, String identifier) {
         this.blockId = blockId;
         this.identifier = identifier;
-        this.id = (short) idCounter.incrementAndGet();
     }
 
     // TODO add another object parameter which will offer a lot of integrated features (like break animation, id change etc...)
@@ -39,6 +33,14 @@ public abstract class CustomBlock {
 
     public abstract UpdateOption getUpdateOption();
 
+    /**
+     * This id can be serialized in chunk file, meaning no duplicate should exist
+     * Changing this value halfway should mean potentially breaking the world
+     *
+     * @return the custom block id
+     */
+    public abstract short getCustomBlockId();
+
     /*
       Time in ms
      */
@@ -59,8 +61,4 @@ public abstract class CustomBlock {
     public String getIdentifier() {
         return identifier;
     }
-
-    public short getId() {
-        return id;
-    }
 }