Check object type in equals

runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java

@@ -190,6 +190,11 @@ public class DFAState {
 	public boolean equals(Object o) {
 		// compare set of ATN configurations in this set with other
 		if ( this==o ) return true;
+
+		if (!(o instanceof DFAState)) {
+			return false;
+		}
+
 		DFAState other = (DFAState)o;
 		// TODO (sam): what to do when configs==null?
 		boolean sameSet = this.configset.equals(other.configset);

runtime/Java/src/org/antlr/v4/runtime/misc/OrderedHashSet.java

@@ -94,6 +94,10 @@ public class OrderedHashSet<T> extends LinkedHashSet<T> {
 
 	@Override
 	public boolean equals(Object o) {
+		if (!(o instanceof OrderedHashSet<?>)) {
+			return false;
+		}
+
 //		System.out.print("equals " + this + ", " + o+" = ");
 		boolean same = elements!=null && elements.equals(((OrderedHashSet<?>)o).elements);
 //		System.out.println(same);

tool/src/org/antlr/v4/codegen/model/decl/AltLabelStructDecl.java

@@ -75,10 +75,8 @@ public class AltLabelStructDecl extends StructDecl {
 	@Override
 	public boolean equals(Object obj) {
 		if ( obj == this ) return true;
-		if ( obj.hashCode() != this.hashCode() ) return false;
-		if ( obj instanceof AltLabelStructDecl ) {
-			return name.equals(((AltLabelStructDecl)obj).name);
-		}
-		return false;
+		if (!(obj instanceof AltLabelStructDecl)) return false;
+
+		return name.equals(((AltLabelStructDecl)obj).name);
 	}
 }

tool/src/org/antlr/v4/codegen/model/decl/Decl.java

@@ -57,11 +57,10 @@ public class Decl extends SrcOp {
 	/** If same name, can't redefine, unless it's a getter */
 	@Override
 	public boolean equals(Object obj) {
-		if ( obj==null ) return false;
+		if ( this==obj ) return true;
+		if ( !(obj instanceof Decl) ) return false;
 		// A() and label A are different
 		if ( obj instanceof ContextGetterDecl ) return false;
-		if ( this==obj ) return true;
-		if ( this.hashCode() != obj.hashCode() ) return false;
 		return name.equals(((Decl) obj).name);
 	}
 }

tool/src/org/antlr/v4/tool/Rule.java

@@ -332,7 +332,15 @@ public class Rule implements AttributeResolver {
 
 	@Override
 	public boolean equals(Object obj) {
-		return this==obj || name.equals(((Rule)obj).name);
+		if (this == obj) {
+			return true;
+		}
+
+		if (!(obj instanceof Rule)) {
+			return false;
+		}
+
+		return name.equals(((Rule)obj).name);
 	}
 
 	@Override