Transition classes override getSerializationType()

runtime/Java/src/org/antlr/v4/runtime/atn/ActionTransition.java

@@ -47,6 +47,11 @@ public class ActionTransition extends Transition {
 		this.isCtxDependent = isCtxDependent;
 	}
 
+	@Override
+	public int getSerializationType() {
+		return ACTION;
+	}
+
 	@Override
 	public boolean isEpsilon() {
 		return true; // we are to be ignored by analysis 'cept for predicates

runtime/Java/src/org/antlr/v4/runtime/atn/AtomTransition.java

@@ -42,6 +42,11 @@ public class AtomTransition extends Transition {
 		this.label = label;
 	}
 
+	@Override
+	public int getSerializationType() {
+		return ATOM;
+	}
+
 	@Override
 	@NotNull
 	public IntervalSet label() { return IntervalSet.of(label); }

runtime/Java/src/org/antlr/v4/runtime/atn/EpsilonTransition.java

@@ -34,6 +34,11 @@ import org.antlr.v4.runtime.misc.NotNull;
 public class EpsilonTransition extends Transition {
 	public EpsilonTransition(@NotNull ATNState target) { super(target); }
 
+	@Override
+	public int getSerializationType() {
+		return EPSILON;
+	}
+
 	@Override
 	public boolean isEpsilon() { return true; }
 

runtime/Java/src/org/antlr/v4/runtime/atn/NotSetTransition.java

@@ -38,6 +38,11 @@ public class NotSetTransition extends SetTransition {
 		super(target, set);
 	}
 
+	@Override
+	public int getSerializationType() {
+		return NOT_SET;
+	}
+
 	@Override
 	public String toString() {
 		return '~'+super.toString();

runtime/Java/src/org/antlr/v4/runtime/atn/PredicateTransition.java

@@ -49,6 +49,11 @@ public class PredicateTransition extends Transition {
 		this.isCtxDependent = isCtxDependent;
 	}
 
+	@Override
+	public int getSerializationType() {
+		return PREDICATE;
+	}
+
 	@Override
 	public boolean isEpsilon() { return true; }
 

runtime/Java/src/org/antlr/v4/runtime/atn/RangeTransition.java

@@ -42,6 +42,11 @@ public class RangeTransition extends Transition {
 		this.to = to;
 	}
 
+	@Override
+	public int getSerializationType() {
+		return RANGE;
+	}
+
 	@Override
 	@NotNull
 	public IntervalSet label() { return IntervalSet.of(from, to); }

runtime/Java/src/org/antlr/v4/runtime/atn/RuleTransition.java

@@ -49,6 +49,11 @@ public class RuleTransition extends Transition {
 		this.followState = followState;
 	}
 
+	@Override
+	public int getSerializationType() {
+		return RULE;
+	}
+
 	@Override
 	public boolean isEpsilon() { return true; }
 }

runtime/Java/src/org/antlr/v4/runtime/atn/SetTransition.java

@@ -46,6 +46,11 @@ public class SetTransition extends Transition {
 		this.set = set;
 	}
 
+	@Override
+	public int getSerializationType() {
+		return SET;
+	}
+
 	@Override
 	@NotNull
 	public IntervalSet label() { return set; }

runtime/Java/src/org/antlr/v4/runtime/atn/Transition.java

@@ -99,7 +99,7 @@ public abstract class Transition {
 		this.target = target;
 	}
 
-	public int getSerializationType() { return 0; }
+	public abstract int getSerializationType();
 
 	/** Are we epsilon, action, sempred? */
 	public boolean isEpsilon() { return false; }

runtime/Java/src/org/antlr/v4/runtime/atn/WildcardTransition.java

@@ -34,6 +34,11 @@ import org.antlr.v4.runtime.misc.NotNull;
 public class WildcardTransition extends Transition {
 	public WildcardTransition(@NotNull ATNState target) { super(target); }
 
+	@Override
+	public int getSerializationType() {
+		return WILDCARD;
+	}
+
 	@Override
 	@NotNull
 	public String toString() {