Interval: make public fields final

The class docs already state that Interval is immutable, but this is not enforced.
Followup to #4901

Signed-off-by: Steven Schlansker <[email protected]>

Author: stevenschlansker

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

@@ -9,8 +9,8 @@
 public class Interval {
 	public static final Interval INVALID = new Interval(-1,-2);
 
-	public int a;
-	public int b;
+	public final int a;
+	public final int b;
 
 	public Interval(int a, int b) { this.a=a; this.b=b; }
 

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

@@ -664,18 +664,21 @@ public void remove(int el) {
             }
             // if on left edge x..b, adjust left
             if ( el==a ) {
-                I.a++;
+                I = Interval.of(a+1, b);
+                intervals.set(i, I);
                 break;
             }
             // if on right edge a..x, adjust right
             if ( el==b ) {
-                I.b--;
+                I = Interval.of(a, b-1);
+                intervals.set(i, I);
                 break;
             }
             // if in middle a..x..b, split interval
             if ( el>a && el<b ) { // found in this interval
                 int oldb = I.b;
-                I.b = el-1;      // [a..x-1]
+                I = Interval.of(a, el-1); // [a..x-1]
+                intervals.set(i, I);
                 add(el+1, oldb); // add [x+1..b]
             }
         }

tool/src/org/antlr/v4/parse/ANTLRLexer.g

@@ -699,7 +699,7 @@ UNICODE_ESC
 				Interval badRange = Interval.of(getCharIndex()-2-hCount, getCharIndex());
 				String lastChar = input.substring(badRange.b, badRange.b);
 				if ( lastChar.codePointAt(0)=='\'' ) {
-					badRange.b--;
+					badRange = Interval.of(badRange.a, badRange.b-1);
 				}
 				String bad = input.substring(badRange.a, badRange.b);
 				Token t = new CommonToken(input, state.type, state.channel, badRange.a, badRange.b);