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Jenson3210jevanlingentimtebeek
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Refine switch cases (#749)
* Refine switch cases * Re-adding no-op block * renamed case -> case_ * Update src/main/java/org/openrewrite/java/migrate/lang/RefineSwitchCases.java Co-authored-by: Jacob van Lingen <jacobvanlingen@hotmail.com> * Update src/main/java/org/openrewrite/java/migrate/lang/RefineSwitchCases.java Co-authored-by: Jacob van Lingen <jacobvanlingen@hotmail.com> * empty one-line J.Blocks * no overhead method call * Minor polish * Show problematic test case * Avoid problematic case by checking for existing guard * Avoid needless calculation of label variables if there's no `if` * Handle unexpected elements in `getConditionVariables` * Rename methods to show intent, as they are not simple `get` methods * Use `Set` and `containsAll` * Prefer to keep body on next line, for a smaller easier diff --------- Co-authored-by: Jacob van Lingen <jacobvanlingen@hotmail.com> Co-authored-by: Tim te Beek <tim@moderne.io>
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‎src/main/java/org/openrewrite/java/migrate/lang/RefineSwitchCases.java‎

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/*
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* Copyright 2025 the original author or authors.
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* <p>
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* Licensed under the Moderne Source Available License (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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* <p>
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* https://docs.moderne.io/licensing/moderne-source-available-license
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* <p>
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.openrewrite.java.migrate.lang;
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import lombok.EqualsAndHashCode;
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import lombok.Value;
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import org.openrewrite.*;
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import org.openrewrite.internal.ListUtils;
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import org.openrewrite.java.JavaIsoVisitor;
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import org.openrewrite.java.tree.Expression;
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import org.openrewrite.java.tree.J;
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import org.openrewrite.java.tree.Space;
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import org.openrewrite.java.tree.Statement;
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import org.openrewrite.staticanalysis.kotlin.KotlinFileChecker;
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Set;
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import static java.util.Collections.singletonList;
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import static java.util.stream.Collectors.toSet;
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import static org.openrewrite.java.tree.J.Block.createEmptyBlock;
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@Value
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@EqualsAndHashCode(callSuper = false)
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public class RefineSwitchCases extends Recipe {
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@Override
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public String getDisplayName() {
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return "Use switch cases refinement when possible";
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}
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@Override
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public String getDescription() {
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return "Use guarded switch case labels and guards if all the statements in the switch block do if/else if/else on the guarded label.";
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}
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@Override
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public TreeVisitor<?, ExecutionContext> getVisitor() {
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return Preconditions.check(Preconditions.not(new KotlinFileChecker<>()), new JavaIsoVisitor<ExecutionContext>() {
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@Override
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public J.Switch visitSwitch(J.Switch sw, ExecutionContext ctx) {
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J.Switch switch_ = super.visitSwitch(sw, ctx);
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J.Switch mappedSwitch = switch_.withCases(switch_.getCases()
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.withStatements(ListUtils.flatMap(switch_.getCases().getStatements(), statement -> {
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if (statement instanceof J.Case) {
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J.Case case_ = (J.Case) statement;
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if (!(case_.getBody() instanceof J.Block) || case_.getGuard() != null) {
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return statement;
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}
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List<Statement> caseStatements = ((J.Block) case_.getBody()).getStatements();
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if (caseStatements.size() == 1 && caseStatements.get(0) instanceof J.If) {
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J.If if_ = (J.If) caseStatements.get(0);
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if (extractLabelVariables(case_)
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.containsAll(extractConditionVariables(if_.getIfCondition().getTree()))) {
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// Replace case with multiple cases
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return createGuardedCases(case_, if_);
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}
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}
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}
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return statement;
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})));
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return new JavaIsoVisitor<ExecutionContext>() {
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@Override
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public J.Case visitCase(J.Case case_, ExecutionContext ctx) {
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// Remove any trailing new line in empty case body
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if (case_.getBody() instanceof J.Block) {
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J.Block body = (J.Block) case_.getBody();
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if (body.getStatements().isEmpty() && !body.getEnd().isEmpty()) {
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return case_.withBody(body.withEnd(Space.EMPTY));
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}
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}
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return case_;
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}
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}.visitSwitch(maybeAutoFormat(switch_, mappedSwitch, ctx), ctx);
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}
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private Set<String> extractLabelVariables(J.Case case_) {
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return case_.getCaseLabels().stream()
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.filter(J.VariableDeclarations.class::isInstance)
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.map(J.VariableDeclarations.class::cast)
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.map(J.VariableDeclarations::getVariables)
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.flatMap(List::stream)
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.map(J.VariableDeclarations.NamedVariable::getName)
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.map(J.Identifier::getSimpleName)
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.collect(toSet());
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}
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private Set<String> extractConditionVariables(Expression expression) {
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return new JavaIsoVisitor<Set<String>>() {
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@Override
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public J.Identifier visitIdentifier(J.Identifier identifier, Set<String> identifiers) {
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identifiers.add(identifier.getSimpleName());
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return super.visitIdentifier(identifier, identifiers);
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}
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@Override
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public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, Set<String> identifiers) {
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// Do not pull out method name as identifier, just any select and arguments
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super.visit(method.getSelect(), identifiers);
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method.getArguments().forEach(arg -> super.visit(arg, identifiers));
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return method;
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}
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}.reduce(expression, new HashSet<>());
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}
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private List<J.Case> createGuardedCases(J.Case case_, J.If if_) {
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if (case_.getBody() == null) {
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return singletonList(case_);
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}
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List<J.Case> cases = new ArrayList<>();
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Statement caseBody = if_.getThenPart();
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if (caseBody instanceof J.Block && ((J.Block) caseBody).getStatements().size() == 1) {
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caseBody = ((J.Block) caseBody).getStatements().get(0);
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}
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cases.add(case_.withId(Tree.randomId()).withGuard(if_.getIfCondition().getTree().withPrefix(Space.SINGLE_SPACE)).withBody(caseBody));
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if (if_.getElsePart() == null) {
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if (case_.getBody() instanceof J.Block) {
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cases.add(case_.withBody(createEmptyBlock().withPrefix(Space.SINGLE_SPACE)));
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}
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} else if (if_.getElsePart().getBody() instanceof J.If) {
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cases.addAll(createGuardedCases(case_, (J.If) if_.getElsePart().getBody()));
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} else {
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cases.add(case_.withBody(if_.getElsePart().getBody()));
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}
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return cases;
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}
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});
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}
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}

‎src/main/resources/META-INF/rewrite/java-version-21.yml‎

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type: specs.openrewrite.org/v1beta/recipe
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name: org.openrewrite.java.migrate.SwitchPatternMatching
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displayName: Adopt switch pattern matching (JEP 441)
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description: "[JEP 441](https://openjdk.org/jeps/441) describes how some switch statements can be improved with pattern matching."
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description: ->-
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[JEP 441](https://openjdk.org/jeps/441) describes how some switch statements can be improved with pattern matching.
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This recipe applies some of those improvements where applicable.
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tags:
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- java21
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recipeList:
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- org.openrewrite.java.migrate.lang.RefineSwitchCases
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- org.openrewrite.java.migrate.lang.SwitchCaseEnumGuardToLabel

‎src/test/java/org/openrewrite/java/migrate/lang/RefineSwitchCasesTest.java‎

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/*
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* Copyright 2025 the original author or authors.
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* <p>
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* Licensed under the Moderne Source Available License (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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* <p>
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* https://docs.moderne.io/licensing/moderne-source-available-license
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* <p>
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.openrewrite.java.migrate.lang;
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import org.junit.jupiter.api.Test;
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import org.openrewrite.DocumentExample;
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import org.openrewrite.test.RecipeSpec;
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import org.openrewrite.test.RewriteTest;
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import static org.openrewrite.java.Assertions.java;
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class RefineSwitchCasesTest implements RewriteTest {
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@Override
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public void defaults(RecipeSpec spec) {
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spec.recipe(new RefineSwitchCases());
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}
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@Test
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@DocumentExample
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void refineCases() {
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rewriteRun(
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//language=java
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java(
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case null -> System.out.println("You did not enter the test yet");
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case Integer i -> {
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if (i >= 5 && i <= 10)
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System.out.println("You got it");
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else if (i >= 0 && i < 5)
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System.out.println("Shame");
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else
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System.out.println("Sorry?");
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}
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case String s -> {
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if (s.equalsIgnoreCase("YES"))
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System.out.println("You got it");
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else if ("NO".equalsIgnoreCase(s))
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System.out.println("Shame");
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else
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System.out.println("Sorry?");
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}
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}
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}
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}
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""",
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case null -> System.out.println("You did not enter the test yet");
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case Integer i when i >= 5 && i <= 10 ->
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System.out.println("You got it");
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case Integer i when i >= 0 && i < 5 ->
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System.out.println("Shame");
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case Integer i ->
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System.out.println("Sorry?");
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case String s when s.equalsIgnoreCase("YES") ->
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System.out.println("You got it");
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case String s when "NO".equalsIgnoreCase(s) ->
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System.out.println("Shame");
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case String s ->
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System.out.println("Sorry?");
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}
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}
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}
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"""
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)
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);
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}
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@Test
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void preferExpressionUsage() {
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rewriteRun(
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//language=java
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java(
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case null -> System.out.println("You did not enter the test yet");
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case Integer i -> {
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if (i >= 5 && i <= 10)
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System.out.println("You got it");
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else if (i >= 0 && i < 5) {
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System.out.println("Shame");
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} else
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System.out.println("Sorry?");
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}
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case String s -> {
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System.out.println("You got it");
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}
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}
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}
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}
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""",
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case null -> System.out.println("You did not enter the test yet");
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case Integer i when i >= 5 && i <= 10 ->
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System.out.println("You got it");
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case Integer i when i >= 0 && i < 5 ->
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System.out.println("Shame");
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case Integer i ->
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System.out.println("Sorry?");
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case String s -> {
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System.out.println("You got it");
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}
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}
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}
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}
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"""
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)
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);
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}
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@Test
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void emptyBlockToAvoidDefault() {
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rewriteRun(
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//language=java
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java(
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case Integer i -> {
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if (i >= 5 && i <= 10)
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System.out.println("You got it");
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else if (i >= 0 && i < 5) {
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System.out.println("Shame");
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}
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}
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default -> System.out.println("Sorry?");
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}
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}
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}
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""",
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case Integer i when i >= 5 && i <= 10 ->
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System.out.println("You got it");
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case Integer i when i >= 0 && i < 5 ->
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System.out.println("Shame");
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case Integer i -> {}
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default -> System.out.println("Sorry?");
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}
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}
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}
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"""
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)
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);
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}
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@Test
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void fieldReference() {
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rewriteRun(
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//language=java
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java(
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case null -> System.out.println("You did not enter the test yet");
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case Integer i -> {
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if (i >= 5 && i <= 10)
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System.out.println("You got it");
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else if (i >= 0 && i < Integer.MAX_VALUE)
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System.out.println("Shame");
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else
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System.out.println("Sorry?");
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}
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}
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}
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}
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""",
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case null -> System.out.println("You did not enter the test yet");
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case Integer i when i >= 5 && i <= 10 ->
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System.out.println("You got it");
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case Integer i when i >= 0 && i < Integer.MAX_VALUE ->
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System.out.println("Shame");
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case Integer i ->
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System.out.println("Sorry?");
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}
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}
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}
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"""
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)
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);
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}
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@Test
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void noChangeWhenAlreadyGuarded() {
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rewriteRun(
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//language=java
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java(
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"""
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class Test {
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static void score(Object obj) {
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switch (obj) {
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case Integer i when i == 7 -> {
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if (i >= 5 && i <= 10)
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System.out.println("You got it");
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else if (i >= 0 && i < 5)
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System.out.println("Shame");
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else
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System.out.println("Sorry?");
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}
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}
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}
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}
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"""
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)
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);
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}
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}

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