8214114: Switch expressions with try-catch statements
Summary: When switch expression contains try-catch, move the stack values into locals before the executing the switch expression, and back when it is done.
Reviewed-by: mcimadamore, vromero
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java Tue Dec 11 08:05:38 2018 +0800
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java Tue Dec 11 09:10:24 2018 +0100
@@ -1121,7 +1121,7 @@
public void visitVarDef(JCVariableDecl tree) {
// Local variables have not been entered yet, so we need to do it now:
- if (env.info.scope.owner.kind == MTH) {
+ if (env.info.scope.owner.kind == MTH || env.info.scope.owner.kind == VAR) {
if (tree.sym != null) {
// parameters have already been entered
env.info.scope.enter(tree.sym);
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java Tue Dec 11 08:05:38 2018 +0800
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java Tue Dec 11 09:10:24 2018 +0100
@@ -1633,7 +1633,7 @@
protected boolean trackable(VarSymbol sym) {
return
sym.pos >= startPos &&
- ((sym.owner.kind == MTH ||
+ ((sym.owner.kind == MTH || sym.owner.kind == VAR ||
isFinalUninitializedField(sym)));
}
@@ -2009,7 +2009,7 @@
lint = lint.augment(tree.sym);
try{
boolean track = trackable(tree.sym);
- if (track && tree.sym.owner.kind == MTH) {
+ if (track && (tree.sym.owner.kind == MTH || tree.sym.owner.kind == VAR)) {
newVar(tree);
}
if (tree.init != null) {
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Gen.java Tue Dec 11 08:05:38 2018 +0800
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Gen.java Tue Dec 11 09:10:24 2018 +0100
@@ -25,8 +25,6 @@
package com.sun.tools.javac.jvm;
-import java.util.function.BiConsumer;
-
import com.sun.tools.javac.tree.TreeInfo.PosKind;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
@@ -166,6 +164,7 @@
boolean inCondSwitchExpression;
Chain switchExpressionTrueChain;
Chain switchExpressionFalseChain;
+ List<LocalItem> stackBeforeSwitchExpression;
/** Generate code to load an integer constant.
* @param n The integer to be loaded.
@@ -1178,13 +1177,59 @@
}
private void doHandleSwitchExpression(JCSwitchExpression tree) {
- int prevLetExprStart = code.setLetExprStackPos(code.state.stacksize);
+ List<LocalItem> prevStackBeforeSwitchExpression = stackBeforeSwitchExpression;
+ int limit = code.nextreg;
try {
- handleSwitch(tree, tree.selector, tree.cases);
+ stackBeforeSwitchExpression = List.nil();
+ if (hasTry(tree)) {
+ //if the switch expression contains try-catch, the catch handlers need to have
+ //an empty stack. So stash whole stack to local variables, and restore it before
+ //breaks:
+ while (code.state.stacksize > 0) {
+ Type type = code.state.peek();
+ Name varName = names.fromString(target.syntheticNameChar() +
+ "stack" +
+ target.syntheticNameChar() +
+ tree.pos +
+ target.syntheticNameChar() +
+ code.state.stacksize);
+ VarSymbol var = new VarSymbol(Flags.SYNTHETIC, varName, type,
+ this.env.enclMethod.sym);
+ LocalItem item = items.new LocalItem(type, code.newLocal(var));
+ stackBeforeSwitchExpression = stackBeforeSwitchExpression.prepend(item);
+ item.store();
+ }
+ }
+ int prevLetExprStart = code.setLetExprStackPos(code.state.stacksize);
+ try {
+ handleSwitch(tree, tree.selector, tree.cases);
+ } finally {
+ code.setLetExprStackPos(prevLetExprStart);
+ }
} finally {
- code.setLetExprStackPos(prevLetExprStart);
+ stackBeforeSwitchExpression = prevStackBeforeSwitchExpression;
+ code.endScopes(limit);
}
}
+ //where:
+ private boolean hasTry(JCSwitchExpression tree) {
+ boolean[] hasTry = new boolean[1];
+ new TreeScanner() {
+ @Override
+ public void visitTry(JCTry tree) {
+ hasTry[0] = true;
+ }
+
+ @Override
+ public void visitClassDef(JCClassDecl tree) {
+ }
+
+ @Override
+ public void visitLambda(JCLambda tree) {
+ }
+ }.scan(tree);
+ return hasTry[0];
+ }
private void handleSwitch(JCTree swtch, JCExpression selector, List<JCCase> cases) {
int limit = code.nextreg;
@@ -1659,14 +1704,17 @@
}
public void visitBreak(JCBreak tree) {
- int tmpPos = code.pendingStatPos;
Assert.check(code.isStatementStart());
- Env<GenContext> targetEnv = unwind(tree.target, env);
- code.pendingStatPos = tmpPos;
+ final Env<GenContext> targetEnv;
if (tree.isValueBreak()) {
+ //restore stack as it was before the switch expression:
+ for (LocalItem li : stackBeforeSwitchExpression) {
+ li.load();
+ }
if (inCondSwitchExpression) {
CondItem value = genCond(tree.value, CRT_FLOW_TARGET);
Chain falseJumps = value.jumpFalse();
+ targetEnv = unwindBreak(tree);
code.resolve(value.trueJumps);
Chain trueJumps = code.branch(goto_);
if (switchExpressionTrueChain == null) {
@@ -1684,13 +1732,22 @@
} else {
genExpr(tree.value, pt).load();
code.state.forceStackTop(tree.target.type);
+ targetEnv = unwindBreak(tree);
targetEnv.info.addExit(code.branch(goto_));
}
} else {
+ targetEnv = unwindBreak(tree);
targetEnv.info.addExit(code.branch(goto_));
}
endFinalizerGaps(env, targetEnv);
}
+ //where:
+ private Env<GenContext> unwindBreak(JCBreak tree) {
+ int tmpPos = code.pendingStatPos;
+ Env<GenContext> targetEnv = unwind(tree.target, env);
+ code.pendingStatPos = tmpPos;
+ return targetEnv;
+ }
public void visitContinue(JCContinue tree) {
int tmpPos = code.pendingStatPos;
@@ -2138,7 +2195,7 @@
res = items.makeMemberItem(sym, true);
}
result = res;
- } else if (sym.kind == VAR && sym.owner.kind == MTH) {
+ } else if (sym.kind == VAR && (sym.owner.kind == MTH || sym.owner.kind == VAR)) {
result = items.makeLocalItem((VarSymbol)sym);
} else if (isInvokeDynamic(sym)) {
result = items.makeDynamicItem(sym);
--- a/test/langtools/tools/javac/switchexpr/ExpressionSwitchBugs.java Tue Dec 11 08:05:38 2018 +0800
+++ b/test/langtools/tools/javac/switchexpr/ExpressionSwitchBugs.java Tue Dec 11 09:10:24 2018 +0100
@@ -23,7 +23,7 @@
/*
* @test
- * @bug 8206986 8214529
+ * @bug 8206986 8214114 8214529
* @summary Verify various corner cases with nested switch expressions.
* @compile --enable-preview -source 12 ExpressionSwitchBugs.java
* @run main/othervm --enable-preview ExpressionSwitchBugs
@@ -33,6 +33,7 @@
public static void main(String... args) {
new ExpressionSwitchBugs().testNested();
new ExpressionSwitchBugs().testAnonymousClasses();
+ new ExpressionSwitchBugs().testFields();
}
private void testNested() {
@@ -84,6 +85,33 @@
}
}
+ private void testFields() {
+ check(3, field);
+ check(3, ExpressionSwitchBugs.staticField);
+ }
+
+ private final int value = 2;
+ private final int field = id(switch(value) {
+ case 0 -> -1;
+ case 2 -> {
+ int temp = 0;
+ temp += 3;
+ break temp;
+ }
+ default -> throw new IllegalStateException();
+ });
+
+ private static final int staticValue = 2;
+ private static final int staticField = new ExpressionSwitchBugs().id(switch(staticValue) {
+ case 0 -> -1;
+ case 2 -> {
+ int temp = 0;
+ temp += 3;
+ break temp;
+ }
+ default -> throw new IllegalStateException();
+ });
+
private int id(int i) {
return i;
}
--- a/test/langtools/tools/javac/switchexpr/ExpressionSwitchEmbedding.java Tue Dec 11 08:05:38 2018 +0800
+++ b/test/langtools/tools/javac/switchexpr/ExpressionSwitchEmbedding.java Tue Dec 11 09:10:24 2018 +0100
@@ -23,7 +23,7 @@
/*
* @test
- * @bug 8214031
+ * @bug 8214031 8214114
* @summary Verify switch expressions embedded in various statements work properly.
* @compile --enable-preview -source 12 ExpressionSwitchEmbedding.java
* @run main/othervm --enable-preview ExpressionSwitchEmbedding
@@ -66,6 +66,50 @@
{
int i = 6;
int o = 0;
+ while (switch (i) {
+ case 1: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 0; break true; }
+ case 2: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 1; break true; }
+ case 3, 4:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ if (i == 2 || i == 4) {
+ try {
+ break switch (i) {
+ case 2 -> throw new ResultException(true);
+ case 4 -> false;
+ default -> throw new IllegalStateException();
+ };
+ } catch (ResultException ex) {
+ break ex.result;
+ }
+ } else {
+ break true;
+ }
+ }
+ default:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ break switch (i) {
+ case -1 -> false;
+ case 3 -> true;
+ default -> true;
+ };
+ }
+ throw new AssertionError();
+ }) {
+ o++;
+ }
+ if (o != 6 && i >= 0) {
+ throw new IllegalStateException();
+ }
+ }
+ {
+ int i = 6;
+ int o = 0;
if (switch (i) {
case 1: i = 0; break true;
case 2: i = 1; break true;
@@ -92,6 +136,50 @@
}
}
{
+ int i = 6;
+ int o = 0;
+ if (switch (i) {
+ case 1: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 0; break true; }
+ case 2: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 1; break true; }
+ case 3, 4:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ if (i == 2 || i == 4) {
+ try {
+ break switch (i) {
+ case 2 -> throw new ResultException(true);
+ case 4 -> false;
+ default -> throw new IllegalStateException();
+ };
+ } catch (ResultException ex) {
+ break ex.result;
+ }
+ } else {
+ break true;
+ }
+ }
+ default:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ break switch (i) {
+ case -1 -> false;
+ case 3 -> true;
+ default -> true;
+ };
+ }
+ throw new AssertionError();
+ }) {
+ o++;
+ }
+ if (o != 1 && i != 5) {
+ throw new IllegalStateException();
+ }
+ }
+ {
int o = 0;
for (int i = 6; (switch (i) {
case 1: i = 0; break true;
@@ -119,6 +207,49 @@
}
}
{
+ int o = 0;
+ for (int i = 6; (switch (i) {
+ case 1: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 0; break true; }
+ case 2: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 1; break true; }
+ case 3, 4:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ if (i == 2 || i == 4) {
+ try {
+ break switch (i) {
+ case 2 -> throw new ResultException(true);
+ case 4 -> false;
+ default -> throw new IllegalStateException();
+ };
+ } catch (ResultException ex) {
+ break ex.result;
+ }
+ } else {
+ break true;
+ }
+ }
+ default:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ break switch (i) {
+ case -1 -> false;
+ case 3 -> true;
+ default -> true;
+ };
+ }
+ throw new AssertionError();
+ }); ) {
+ o++;
+ }
+ if (o != 6) {
+ throw new IllegalStateException();
+ }
+ }
+ {
int i = 6;
int o = 0;
do {
@@ -146,6 +277,60 @@
throw new IllegalStateException();
}
}
+ {
+ int i = 6;
+ int o = 0;
+ do {
+ o++;
+ } while (switch (i) {
+ case 1: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 0; break true; }
+ case 2: try { new ExpressionSwitchEmbedding().throwException(); } catch (Throwable t) { i = 1; break true; }
+ case 3, 4:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ if (i == 2 || i == 4) {
+ try {
+ break switch (i) {
+ case 2 -> throw new ResultException(true);
+ case 4 -> false;
+ default -> throw new IllegalStateException();
+ };
+ } catch (ResultException ex) {
+ break ex.result;
+ }
+ } else {
+ break true;
+ }
+ }
+ default:
+ try {
+ new ExpressionSwitchEmbedding().throwException();
+ } catch (Throwable t) {
+ i--;
+ break switch (i) {
+ case -1 -> false;
+ case 3 -> true;
+ default -> true;
+ };
+ }
+ throw new AssertionError();
+ });
+ if (o != 6 && i >= 0) {
+ throw new IllegalStateException();
+ }
+ }
}
+ private void throwException() {
+ throw new RuntimeException();
+ }
+
+ private static final class ResultException extends RuntimeException {
+ public final boolean result;
+ public ResultException(boolean result) {
+ this.result = result;
+ }
+ }
}
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/test/langtools/tools/javac/switchexpr/TryCatch.java Tue Dec 11 09:10:24 2018 +0100
@@ -0,0 +1,423 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8214114
+ * @summary Verify try-catch inside a switch expression works properly.
+ * @compile --enable-preview -source 12 TryCatch.java
+ * @run main/othervm --enable-preview TryCatch
+ */
+public class TryCatch {
+ public static void main(String[] args) {
+ {
+ int val = 3;
+ for (int p : new int[] {0, 1, 2}) {
+ int res = 1 + new TryCatch().id(switch(p) {
+ case 0 -> switch (p + 1) {
+ case 1:
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ break val;
+ }
+ default: break -1;
+ };
+ case 1 -> {
+ try {
+ break new TryCatch().id(switch (p + 1) {
+ case 2:
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break -1;
+ });
+ } catch(Throwable ex) {
+ break val;
+ }
+ }
+ default -> {
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ break val;
+ }
+ }
+ } - 1);
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+ {
+ int val = 3;
+ for (int p : new int[] {0, 1, 2}) {
+ int x;
+ int res = new TryCatch().id(val == 3 && switch(p) {
+ case 0 -> switch (p + 1) {
+ case 1:
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ break true;
+ }
+ default: break false;
+ };
+ case 1 -> {
+ try {
+ break new TryCatch().id(switch (p + 1) {
+ case 2:
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break false;
+ });
+ } catch(Throwable ex) {
+ break true;
+ }
+ }
+ default -> {
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ break true;
+ }
+ }
+ } && (x = 1) == 1 && x == 1 ? val : -1);
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+ {
+ int val = 3;
+ for (E e : new E[] {E.A, E.B, E.C}) {
+ int res = 1 + new TryCatch().id(switch(e) {
+ case A -> switch (e.next()) {
+ case B:
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ break val;
+ }
+ default: break -1;
+ };
+ case B -> {
+ try {
+ break new TryCatch().id(switch (e.next()) {
+ case C:
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break -1;
+ });
+ } catch(Throwable ex) {
+ break val;
+ }
+ }
+ default -> {
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ break val;
+ }
+ }
+ } - 1);
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+ {
+ int val = 3;
+ for (E e : new E[] {E.A, E.B, E.C}) {
+ int x;
+ int res = new TryCatch().id(val == 3 && switch(e) {
+ case A -> switch (e.next()) {
+ case B:
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ break true;
+ }
+ default: break false;
+ };
+ case B -> {
+ try {
+ break new TryCatch().id(switch (e.next()) {
+ case C:
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break false;
+ });
+ } catch(Throwable ex) {
+ break true;
+ }
+ }
+ default -> {
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ break true;
+ }
+ }
+ } && (x = 1) == 1 && x == 1 ? val : -1);
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+ {
+ int val = 3;
+ for (String s : new String[] {"", "a", "b"}) {
+ int res = 1 + new TryCatch().id(switch(s) {
+ case "" -> switch (s + "c") {
+ case "c":
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ break val;
+ }
+ default: break -1;
+ };
+ case "a" -> {
+ try {
+ break new TryCatch().id(switch (s + "c") {
+ case "ac":
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break -1;
+ });
+ } catch(Throwable ex) {
+ break val;
+ }
+ }
+ default -> {
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ break val;
+ }
+ }
+ } - 1);
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+ {
+ int val = 3;
+ for (String s : new String[] {"", "a", "b"}) {
+ int x;
+ int res = new TryCatch().id(val == 3 && switch(s) {
+ case "" -> switch (s + "c") {
+ case "c":
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ break true;
+ }
+ default: break false;
+ };
+ case "a" -> {
+ try {
+ break new TryCatch().id(switch (s + "c") {
+ case "ac":
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break false;
+ });
+ } catch(Throwable ex) {
+ break true;
+ }
+ }
+ default -> {
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ break true;
+ }
+ }
+ } && (x = 1) == 1 && x == 1 ? val : -1);
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+
+ {
+ int res = new FieldHolder().intTest;
+
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ {
+ int res = FieldHolder.intStaticTest;
+
+ if (res != 3) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ {
+ boolean res = new FieldHolder().booleanTest;
+
+ if (!res) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ {
+ boolean res = FieldHolder.booleanStaticTest;
+
+ if (!res) {
+ throw new AssertionError("Unexpected result: " + res);
+ }
+ }
+ }
+
+ static class FieldHolder {
+ private final int intTest = switch (0) {
+ case -1: break -1;
+ default:
+ try {
+ break new TryCatch().id(switch (2) {
+ case 2:
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break -1;
+ });
+ } catch(Throwable ex) {
+ break 3;
+ }
+ };
+ private static final int intStaticTest = switch (0) {
+ case -1: break -1;
+ default:
+ try {
+ break new TryCatch().id(switch (2) {
+ case 2:
+ try {
+ new TryCatch().throwException();
+ break -1;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break -1;
+ });
+ } catch(Throwable ex) {
+ break 3;
+ }
+ };
+ private final boolean booleanTest = switch (0) {
+ case -1: break false;
+ default:
+ try {
+ break new TryCatch().id(switch (2) {
+ case 2:
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break false;
+ });
+ } catch(Throwable ex) {
+ break true;
+ }
+ };
+ private static final boolean booleanStaticTest = switch (0) {
+ case -1: break false;
+ default:
+ try {
+ break new TryCatch().id(switch (2) {
+ case 2:
+ try {
+ new TryCatch().throwException();
+ break false;
+ } catch(Throwable ex) {
+ throw ex;
+ }
+ default: break false;
+ });
+ } catch(Throwable ex) {
+ break true;
+ }
+ };
+ }
+
+ private int id(int i) {
+ return i;
+ }
+
+ private boolean id(boolean b) {
+ return b;
+ }
+
+ private void throwException() {
+ throw new RuntimeException();
+ }
+ enum E {
+ A, B, C;
+ public E next() {
+ return values()[(ordinal() + 1) % values().length];
+ }
+ }
+}