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Add recipe to migrate System.out.print/println to IO.print/println (#848)
* Add ReplaceSystemOutWithIOPrint to migrate System.out.print/println to IO.print/println * refactor: reformatting * Handle additional edge case with static import * Inline templates * Use markdown * Include with Java 25 upgrade * Do not replace `printf` --------- Co-authored-by: Tim te Beek <[email protected]>
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‎src/main/java/org/openrewrite/java/migrate/io/ReplaceSystemOutWithIOPrint.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.io;
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import org.openrewrite.ExecutionContext;
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import org.openrewrite.Preconditions;
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import org.openrewrite.Recipe;
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import org.openrewrite.TreeVisitor;
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import org.openrewrite.java.JavaIsoVisitor;
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import org.openrewrite.java.JavaTemplate;
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import org.openrewrite.java.MethodMatcher;
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import org.openrewrite.java.search.UsesMethod;
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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.TypeUtils;
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public class ReplaceSystemOutWithIOPrint extends Recipe {
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@Override
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public String getDisplayName() {
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return "Migrate `System.out.print` to Java 25 IO utility class";
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}
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@Override
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public String getDescription() {
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return "Replace `System.out.print()`, `System.out.println()` with `IO.print()` and `IO.println()`. " +
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"Migrates to the new IO utility class introduced in Java 25.";
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}
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private static final MethodMatcher SYSTEM_OUT_PRINT = new MethodMatcher("java.io.PrintStream print(..)");
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private static final MethodMatcher SYSTEM_OUT_PRINTLN = new MethodMatcher("java.io.PrintStream println(..)");
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@Override
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public TreeVisitor<?, ExecutionContext> getVisitor() {
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return Preconditions.check(
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Preconditions.or(
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new UsesMethod<>(SYSTEM_OUT_PRINT),
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new UsesMethod<>(SYSTEM_OUT_PRINTLN)
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),
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new JavaIsoVisitor<ExecutionContext>() {
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@Override
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public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx) {
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J.MethodInvocation m = super.visitMethodInvocation(method, ctx);
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if (!isSystemOutMethod(m)) {
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return m;
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}
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String methodName = m.getName().getSimpleName();
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return m.getArguments().isEmpty() ?
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JavaTemplate.builder("IO.#{}()").build()
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.apply(getCursor(), m.getCoordinates().replace(), methodName) :
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JavaTemplate.builder("IO.#{}(#{any()})").build()
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.apply(getCursor(), m.getCoordinates().replace(), methodName, m.getArguments().get(0));
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}
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private boolean isSystemOutMethod(J.MethodInvocation mi) {
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if (SYSTEM_OUT_PRINT.matches(mi) || SYSTEM_OUT_PRINTLN.matches(mi)) {
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Expression expression = mi.getSelect();
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if (expression instanceof J.FieldAccess) {
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return isSystemOut(((J.FieldAccess) expression).getName());
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}
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if (expression instanceof J.Identifier) {
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maybeRemoveImport("java.lang.System.out");
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return isSystemOut((J.Identifier) expression);
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}
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}
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return false;
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}
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private boolean isSystemOut(J.Identifier identifier) {
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return "out".equals(identifier.getSimpleName()) &&
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identifier.getFieldType() != null &&
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TypeUtils.isAssignableTo("java.lang.System", identifier.getFieldType().getOwner());
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}
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});
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}
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}

‎src/main/resources/META-INF/rewrite/java-version-25.yml‎

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version: 25
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- org.openrewrite.github.SetupJavaUpgradeJavaVersion:
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minimumJavaMajorVersion: 25
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- org.openrewrite.java.migrate.io.ReplaceSystemOutWithIOPrint
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- org.openrewrite.java.migrate.lang.MigrateProcessWaitForDuration
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- org.openrewrite.java.migrate.lang.ReplaceUnusedVariablesWithUnderscore
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- org.openrewrite.java.migrate.util.MigrateInflaterDeflaterToClose

‎src/test/java/org/openrewrite/java/migrate/io/ReplaceSystemOutWithIOPrintTest.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.io;
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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.java.JavaParser;
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import org.openrewrite.java.search.FindMissingTypes;
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import org.openrewrite.test.RecipeSpec;
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import org.openrewrite.test.RewriteTest;
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import org.openrewrite.test.TypeValidation;
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import static org.openrewrite.java.Assertions.java;
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import static org.openrewrite.java.Assertions.javaVersion;
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class ReplaceSystemOutWithIOPrintTest implements RewriteTest {
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@Override
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public void defaults(RecipeSpec spec) {
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spec.recipe(new ReplaceSystemOutWithIOPrint())
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.afterTypeValidationOptions(TypeValidation.all().allowMissingType(o -> {
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assert o instanceof FindMissingTypes.MissingTypeResult;
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FindMissingTypes.MissingTypeResult result = (FindMissingTypes.MissingTypeResult) o;
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return result.getPrintedTree().contains("IO");
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})) // TODO remove once tests run on Java 25+
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.parser(JavaParser.fromJavaVersion())
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.allSources(s -> s.markers(javaVersion(25)));
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}
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@DocumentExample
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@Test
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void replaceSystemOutPrint() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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System.out.print("Hello");
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}
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}
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""",
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"""
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class Example {
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void test() {
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IO.print("Hello");
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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 replaceSystemOutPrintln() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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System.out.println("Hello");
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}
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}
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""",
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"""
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class Example {
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void test() {
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IO.println("Hello");
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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 replaceSystemOutPrintlnWithStaticImport() {
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rewriteRun(
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java(
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"""
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import static java.lang.System.out;
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class Example {
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void test() {
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out.println("Hello");
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}
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}
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""",
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"""
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class Example {
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void test() {
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IO.println("Hello");
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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 replaceSystemOutPrintWithVariable() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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String message = "Hello World";
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System.out.print(message);
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}
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}
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""",
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"""
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class Example {
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void test() {
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String message = "Hello World";
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IO.print(message);
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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 replaceSystemOutPrintlnEmpty() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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System.out.println();
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}
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}
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""",
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"""
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class Example {
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void test() {
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IO.println();
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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 replaceMultipleSystemOutCalls() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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System.out.print("Hello");
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System.out.println(" World");
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System.out.print(42);
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System.out.println();
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}
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}
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""",
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"""
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class Example {
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void test() {
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IO.print("Hello");
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IO.println(" World");
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IO.print(42);
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IO.println();
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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 handlesPrintWithComplexExpressions() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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String name = "John";
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int age = 30;
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System.out.print("Name: " + name + ", Age: " + age);
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System.out.println(String.format("Formatted: %s is %d years old", name, age));
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}
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}
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""",
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"""
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class Example {
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void test() {
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String name = "John";
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int age = 30;
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IO.print("Name: " + name + ", Age: " + age);
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IO.println(String.format("Formatted: %s is %d years old", name, age));
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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 doesNotReplaceSystemErrCalls() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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System.err.print("Error message");
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System.err.println("Error message");
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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 doesNotReplaceOtherPrintStreams() {
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rewriteRun(
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java(
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"""
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import java.io.PrintStream;
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class Example {
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void test() {
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PrintStream ps = new PrintStream(System.out);
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ps.print("Should not change");
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ps.println("Should not change");
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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 doesNotReplacePrintf() {
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rewriteRun(
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java(
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"""
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class Example {
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void test() {
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System.out.printf("Hello%n");
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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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