Merge changes from topic "oct16b"

* changes:
  Recommend efficient String operations.
  Simple alternative to String.format().

apct-tests/perftests/core/src/android/text/TextUtilsPerfTest.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.text;
+
+import android.perftests.utils.BenchmarkState;
+import android.perftests.utils.PerfStatusReporter;
+
+import androidx.test.filters.LargeTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.util.function.Supplier;
+
+@RunWith(AndroidJUnit4.class)
+@LargeTest
+public class TextUtilsPerfTest {
+    @Rule
+    public PerfStatusReporter mPerfStatusReporter = new PerfStatusReporter();
+
+    public static final String TEMPLATE = "Template that combines %s and %d together";
+
+    public String mVar1 = "example";
+    public int mVar2 = 42;
+
+    /**
+     * Measure overhead of formatting a string via {@link String#format}.
+     */
+    @Test
+    public void timeFormatUpstream() {
+        final BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        while (state.keepRunning()) {
+            String res = String.format(TEMPLATE, mVar1, mVar2);
+        }
+    }
+
+    /**
+     * Measure overhead of formatting a string via
+     * {@link TextUtils#formatSimple}.
+     */
+    @Test
+    public void timeFormatLocal() {
+        final BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        while (state.keepRunning()) {
+            String res = TextUtils.formatSimple(TEMPLATE, mVar1, mVar2);
+        }
+    }
+
+    /**
+     * Measure overhead of formatting a string inline.
+     */
+    @Test
+    public void timeFormatInline() {
+        final BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        while (state.keepRunning()) {
+            String res = "Template that combines " + mVar1 + " and " + mVar2 + " together";
+        }
+    }
+
+    /**
+     * Measure overhead of a passing null-check that uses a lambda to
+     * communicate a custom error message.
+     */
+    @Test
+    public void timeFormat_Skip_Lambda() {
+        final BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        while (state.keepRunning()) {
+            requireNonNull(this, () -> {
+                return String.format(TEMPLATE, mVar1, mVar2);
+            });
+        }
+    }
+
+    /**
+     * Measure overhead of a passing null-check that uses varargs to communicate
+     * a custom error message.
+     */
+    @Test
+    public void timeFormat_Skip_Varargs() {
+        final BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        while (state.keepRunning()) {
+            requireNonNull(this, TEMPLATE, mVar1, mVar2);
+        }
+    }
+
+    private static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
+        return obj;
+    }
+
+    private static <T> T requireNonNull(T obj, String format, Object... args) {
+        return obj;
+    }
+}

core/java/android/text/TextUtils.java

@@ -2079,6 +2079,94 @@ public class TextUtils {
         return Resources.getSystem().getQuantityString(R.plurals.selected_count, count, count);
     }
 
+    /**
+     * Simple alternative to {@link String#format} which purposefully supports
+     * only a small handful of substitutions to improve execution speed.
+     * Benchmarking reveals this optimized alternative performs 6.5x faster for
+     * a typical format string.
+     * <p>
+     * Below is a summary of the limited grammar supported by this method; if
+     * you need advanced features, please continue using {@link String#format}.
+     * <ul>
+     * <li>{@code %b} for {@code boolean}
+     * <li>{@code %c} for {@code char}
+     * <li>{@code %d} for {@code int} or {@code long}
+     * <li>{@code %f} for {@code float} or {@code double}
+     * <li>{@code %s} for {@code String}
+     * <li>{@code %x} for hex representation of {@code int} or {@code long}
+     * <li>{@code %%} for literal {@code %}
+     * </ul>
+     *
+     * @throws IllegalArgumentException if the format string or arguments don't
+     *             match the supported grammar described above.
+     * @hide
+     */
+    public static @NonNull String formatSimple(@NonNull String format, Object... args) {
+        final StringBuilder sb = new StringBuilder(format);
+        int j = 0;
+        for (int i = 0; i < sb.length(); ) {
+            if (sb.charAt(i) == '%') {
+                final String repl;
+                final char code = sb.charAt(i + 1);
+                switch (code) {
+                    case 'b': {
+                        if (j == args.length) {
+                            throw new IllegalArgumentException("Too few arguments");
+                        }
+                        final Object arg = args[j++];
+                        if (arg instanceof Boolean) {
+                            repl = Boolean.toString((boolean) arg);
+                        } else {
+                            repl = Boolean.toString(arg != null);
+                        }
+                        break;
+                    }
+                    case 'c':
+                    case 'd':
+                    case 'f':
+                    case 's': {
+                        if (j == args.length) {
+                            throw new IllegalArgumentException("Too few arguments");
+                        }
+                        final Object arg = args[j++];
+                        repl = String.valueOf(arg);
+                        break;
+                    }
+                    case 'x': {
+                        if (j == args.length) {
+                            throw new IllegalArgumentException("Too few arguments");
+                        }
+                        final Object arg = args[j++];
+                        if (arg instanceof Integer) {
+                            repl = Integer.toHexString((int) arg);
+                        } else if (arg instanceof Long) {
+                            repl = Long.toHexString((long) arg);
+                        } else {
+                            throw new IllegalArgumentException(
+                                    "Unsupported hex type " + arg.getClass());
+                        }
+                        break;
+                    }
+                    case '%': {
+                        repl = "%";
+                        break;
+                    }
+                    default: {
+                        throw new IllegalArgumentException("Unsupported format code " + code);
+                    }
+                }
+                sb.replace(i, i + 2, repl);
+                i += repl.length();
+            } else {
+                i++;
+            }
+        }
+        if (j != args.length) {
+            throw new IllegalArgumentException("Too many arguments");
+        }
+        return sb.toString();
+    }
+
     /**
      * Returns whether or not the specified spanned text has a style span.
      * @hide

core/java/com/android/internal/util/Preconditions.java

@@ -31,6 +31,12 @@ import java.util.Objects;
  */
 public class Preconditions {
 
+    /**
+     * Ensures that an expression checking an argument is true.
+     *
+     * @param expression the expression to check
+     * @throws IllegalArgumentException if {@code expression} is false
+     */
     @UnsupportedAppUsage
     public static void checkArgument(boolean expression) {
         if (!expression) {
@@ -62,8 +68,9 @@ public class Preconditions {
      * @param messageArgs arguments for {@code messageTemplate}
      * @throws IllegalArgumentException if {@code expression} is false
      */
-    public static void checkArgument(boolean expression,
-            final String messageTemplate,
+    public static void checkArgument(
+            final boolean expression,
+            final @NonNull String messageTemplate,
             final Object... messageArgs) {
         if (!expression) {
             throw new IllegalArgumentException(String.format(messageTemplate, messageArgs));
@@ -114,7 +121,9 @@ public class Preconditions {
      * @throws IllegalArgumentException if {@code string} is empty
      */
     public static @NonNull <T extends CharSequence> T checkStringNotEmpty(
-            final T string, final String messageTemplate, final Object... messageArgs) {
+            final T string,
+            final @NonNull String messageTemplate,
+            final Object... messageArgs) {
         if (TextUtils.isEmpty(string)) {
             throw new IllegalArgumentException(String.format(messageTemplate, messageArgs));
         }
@@ -160,18 +169,22 @@ public class Preconditions {
     }
 
     /**
-     * Ensures the truth of an expression involving the state of the calling
-     * instance, but not involving any parameters to the calling method.
+     * Ensures that an object reference passed as a parameter to the calling
+     * method is not null.
      *
-     * @param expression a boolean expression
-     * @param message exception message
-     * @throws IllegalStateException if {@code expression} is false
+     * @param messageTemplate a printf-style message template to use if the check fails; will
+     *     be converted to a string using {@link String#format(String, Object...)}
+     * @param messageArgs arguments for {@code messageTemplate}
+     * @throws NullPointerException if {@code reference} is null
      */
-    @UnsupportedAppUsage
-    public static void checkState(final boolean expression, String message) {
-        if (!expression) {
-            throw new IllegalStateException(message);
+    public static @NonNull <T> T checkNotNull(
+            final T reference,
+            final @NonNull String messageTemplate,
+            final Object... messageArgs) {
+        if (reference == null) {
+            throw new NullPointerException(String.format(messageTemplate, messageArgs));
         }
+        return reference;
     }
 
     /**
@@ -186,6 +199,41 @@ public class Preconditions {
         checkState(expression, null);
     }
 
+    /**
+     * Ensures the truth of an expression involving the state of the calling
+     * instance, but not involving any parameters to the calling method.
+     *
+     * @param expression a boolean expression
+     * @param errorMessage the exception message to use if the check fails; will
+     *     be converted to a string using {@link String#valueOf(Object)}
+     * @throws IllegalStateException if {@code expression} is false
+     */
+    @UnsupportedAppUsage
+    public static void checkState(final boolean expression, String errorMessage) {
+        if (!expression) {
+            throw new IllegalStateException(errorMessage);
+        }
+    }
+
+    /**
+     * Ensures the truth of an expression involving the state of the calling
+     * instance, but not involving any parameters to the calling method.
+     *
+     * @param expression a boolean expression
+     * @param messageTemplate a printf-style message template to use if the check fails; will
+     *     be converted to a string using {@link String#format(String, Object...)}
+     * @param messageArgs arguments for {@code messageTemplate}
+     * @throws IllegalStateException if {@code expression} is false
+     */
+    public static void checkState(
+            final boolean expression,
+            final @NonNull String messageTemplate,
+            final Object... messageArgs) {
+        if (!expression) {
+            throw new IllegalStateException(String.format(messageTemplate, messageArgs));
+        }
+    }
+
     /**
      * Ensures the truth of an expression involving whether the calling identity is authorized to
      * call the calling method.

core/tests/coretests/src/android/text/TextUtilsTest.java

@@ -16,6 +16,8 @@
 
 package android.text;
 
+import static android.text.TextUtils.formatSimple;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -794,4 +796,53 @@ public class TextUtilsTest {
         assertEquals("", TextUtils.trimToLengthWithEllipsis("", 3));
         assertNull(TextUtils.trimToLengthWithEllipsis(null, 3));
     }
+
+    @Test
+    public void testFormatSimple_Types() {
+        assertEquals("true", formatSimple("%b", true));
+        assertEquals("false", formatSimple("%b", false));
+        assertEquals("true", formatSimple("%b", this));
+        assertEquals("false", formatSimple("%b", new Object[] { null }));
+
+        assertEquals("!", formatSimple("%c", '!'));
+
+        assertEquals("42", formatSimple("%d", 42));
+        assertEquals("281474976710656", formatSimple("%d", 281474976710656L));
+
+        assertEquals("3.14159", formatSimple("%f", 3.14159));
+        assertEquals("NaN", formatSimple("%f", Float.NaN));
+
+        assertEquals("example", formatSimple("%s", "example"));
+        assertEquals("null", formatSimple("%s", new Object[] { null }));
+
+        assertEquals("2a", formatSimple("%x", 42));
+        assertEquals("1000000000000", formatSimple("%x", 281474976710656L));
+
+        assertEquals("%", formatSimple("%%"));
+    }
+
+    @Test
+    public void testFormatSimple_Empty() {
+        assertEquals("", formatSimple(""));
+    }
+
+    @Test
+    public void testFormatSimple_Typical() {
+        assertEquals("String foobar and %% number -42 together",
+                formatSimple("String %s%s and %%%% number %d%d together", "foo", "bar", -4, 2));
+    }
+
+    @Test
+    public void testFormatSimple_Mismatch() {
+        try {
+            formatSimple("%s");
+            fail();
+        } catch (IllegalArgumentException expected) {
+        }
+        try {
+            formatSimple("%s", "foo", "bar");
+            fail();
+        } catch (IllegalArgumentException expected) {
+        }
+    }
 }

errorprone/java/com/google/errorprone/bugpatterns/android/EfficientStringsChecker.java

@@ -0,0 +1,146 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns.android;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
+import static com.google.errorprone.matchers.Matchers.allOf;
+import static com.google.errorprone.matchers.Matchers.contains;
+import static com.google.errorprone.matchers.Matchers.kindIs;
+import static com.google.errorprone.matchers.Matchers.methodInvocation;
+import static com.google.errorprone.matchers.Matchers.not;
+import static com.google.errorprone.matchers.Matchers.staticMethod;
+
+import com.google.auto.service.AutoService;
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
+import com.google.errorprone.matchers.Description;
+import com.google.errorprone.matchers.Matcher;
+import com.google.errorprone.predicates.TypePredicate;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.LiteralTree;
+import com.sun.source.tree.MethodInvocationTree;
+import com.sun.source.tree.Tree.Kind;
+import com.sun.tools.javac.code.Symbol.VarSymbol;
+import com.sun.tools.javac.code.Type;
+
+import java.util.List;
+
+/**
+ * Android offers several efficient alternatives to some upstream {@link String}
+ * operations.
+ */
+@AutoService(BugChecker.class)
+@BugPattern(
+    name = "AndroidFrameworkEfficientStrings",
+    summary = "Verifies efficient Strings best-practices",
+    severity = WARNING)
+public final class EfficientStringsChecker extends BugChecker
+        implements MethodInvocationTreeMatcher {
+
+    private static final Matcher<ExpressionTree> FORMAT_CALL = methodInvocation(
+            staticMethod().onClass("java.lang.String").named("format"));
+    private static final Matcher<ExpressionTree> PRECONDITIONS_CALL = methodInvocation(
+            staticMethod().onClass(withSimpleName("Preconditions")).withAnyName());
+    private static final Matcher<ExpressionTree> OBJECTS_CALL = methodInvocation(
+            staticMethod().onClass("java.util.Objects").named("requireNonNull"));
+
+    /**
+     * Match an expression which combines both string literals any other dynamic
+     * values, since these allocate a transparent StringBuilder.
+     * <p>
+     * This won't match a single isolated string literal, or a chain consisting
+     * of only string literals, since those don't require dynamic construction.
+     */
+    private static final Matcher<ExpressionTree> CONTAINS_DYNAMIC_STRING = allOf(
+            contains(ExpressionTree.class, kindIs(Kind.STRING_LITERAL)),
+            contains(ExpressionTree.class, not(kindIs(Kind.STRING_LITERAL))));
+
+    @Override
+    public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
+        if (FORMAT_CALL.matches(tree, state)) {
+            // Skip over possible locale to find format string
+            final List<? extends ExpressionTree> args = tree.getArguments();
+            final ExpressionTree formatArg;
+            final List<VarSymbol> vars = ASTHelpers.getSymbol(tree).params();
+            if (vars.get(0).type.toString().equals("java.util.Locale")) {
+                formatArg = args.get(1);
+            } else {
+                formatArg = args.get(0);
+            }
+
+            // Determine if format string is "simple" enough to replace
+            if (formatArg.getKind() == Kind.STRING_LITERAL) {
+                final String format = String.valueOf(((LiteralTree) formatArg).getValue());
+                if (isSimple(format)) {
+                    return buildDescription(formatArg)
+                            .setMessage("Simple format strings can be replaced with "
+                                    + "TextUtils.formatSimple() for a 6x performance improvement")
+                            .build();
+                }
+            }
+        } else if (PRECONDITIONS_CALL.matches(tree, state)
+                || OBJECTS_CALL.matches(tree, state)) {
+            final List<? extends ExpressionTree> args = tree.getArguments();
+            for (int i = 1 ; i < args.size(); i++) {
+                final ExpressionTree arg = args.get(i);
+                if (CONTAINS_DYNAMIC_STRING.matches(arg, state)) {
+                    return buildDescription(arg)
+                            .setMessage("Building dynamic messages is discouraged, since they "
+                                    + "always allocate a transparent StringBuilder, even in "
+                                    + "the successful case")
+                            .build();
+                }
+            }
+        }
+        return Description.NO_MATCH;
+    }
+
+    static boolean isSimple(String format) {
+        for (int i = 0; i < format.length(); i++) {
+            char c = format.charAt(i);
+            if (c == '%') {
+                i++;
+                c = format.charAt(i);
+                switch (c) {
+                    case 'b':
+                    case 'c':
+                    case 'd':
+                    case 'f':
+                    case 's':
+                    case 'x':
+                    case '%':
+                        break;
+                    default:
+                        return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    static TypePredicate withSimpleName(final String filter) {
+        return new TypePredicate() {
+            @Override
+            public boolean apply(Type type, VisitorState state) {
+                return type.tsym.getSimpleName().toString().equals(filter);
+            }
+        };
+    }
+}

errorprone/tests/java/com/google/errorprone/bugpatterns/android/EfficientStringsCheckerTest.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.errorprone.bugpatterns.android;
+
+import static junit.framework.Assert.assertFalse;
+import static junit.framework.Assert.assertTrue;
+
+import com.google.errorprone.CompilationTestHelper;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class EfficientStringsCheckerTest {
+    private CompilationTestHelper compilationHelper;
+
+    @Before
+    public void setUp() {
+        compilationHelper = CompilationTestHelper.newInstance(
+                EfficientStringsChecker.class, getClass());
+    }
+
+    @Test
+    public void testSimple() {
+        assertTrue(EfficientStringsChecker.isSimple(""));
+        assertTrue(EfficientStringsChecker.isSimple("%s"));
+        assertTrue(EfficientStringsChecker.isSimple("String %s%s and %%%% number %d%d together"));
+
+        assertFalse(EfficientStringsChecker.isSimple("%04d"));
+        assertFalse(EfficientStringsChecker.isSimple("%02x:%02x:%02x"));
+    }
+
+    @Test
+    public void testFormat() {
+        compilationHelper
+                .addSourceLines("Example.java",
+                        "import java.util.Locale;",
+                        "public class Example {",
+                        "  public void example(String str) {",
+                        "    String.format(str, str);",
+                        "    // BUG: Diagnostic contains:",
+                        "    String.format(\"foo %s bar\", str);",
+                        "    // BUG: Diagnostic contains:",
+                        "    String.format(\"foo %d bar\", 42);",
+                        "    String.format(\"foo %04d bar\", 42);",
+                        "  }",
+                        "  public void exampleLocale(String str) {",
+                        "    String.format(Locale.US, str, str);",
+                        "    // BUG: Diagnostic contains:",
+                        "    String.format(Locale.US, \"foo %s bar\", str);",
+                        "    // BUG: Diagnostic contains:",
+                        "    String.format(Locale.US, \"foo %d bar\", 42);",
+                        "    String.format(Locale.US, \"foo %04d bar\", 42);",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+
+    @Test
+    public void testPreconditions() {
+        compilationHelper
+                .addSourceFile("/android/util/Preconditions.java")
+                .addSourceLines("Example.java",
+                        "import android.util.Preconditions;",
+                        "import java.util.Objects;",
+                        "public class Example {",
+                        "  String str;",
+                        "  public void checkState(boolean val) {",
+                        "    Preconditions.checkState(val);",
+                        "    Preconditions.checkState(val, str);",
+                        "    Preconditions.checkState(val, \"foo\");",
+                        "    Preconditions.checkState(val, \"foo\" + \"bar\");",
+                        "    // BUG: Diagnostic contains:",
+                        "    Preconditions.checkState(val, \"foo \" + val);",
+                        "  }",
+                        "  public void checkArgument(boolean val) {",
+                        "    Preconditions.checkArgument(val);",
+                        "    Preconditions.checkArgument(val, str);",
+                        "    Preconditions.checkArgument(val, \"foo\");",
+                        "    Preconditions.checkArgument(val, \"foo\" + \"bar\");",
+                        "    // BUG: Diagnostic contains:",
+                        "    Preconditions.checkArgument(val, \"foo \" + val);",
+                        "  }",
+                        "  public void checkNotNull(Object val) {",
+                        "    Preconditions.checkNotNull(val);",
+                        "    Preconditions.checkNotNull(val, str);",
+                        "    Preconditions.checkNotNull(val, \"foo\");",
+                        "    Preconditions.checkNotNull(val, \"foo\" + \"bar\");",
+                        "    // BUG: Diagnostic contains:",
+                        "    Preconditions.checkNotNull(val, \"foo \" + val);",
+                        "  }",
+                        "  public void requireNonNull(Object val) {",
+                        "    Objects.requireNonNull(val);",
+                        "    Objects.requireNonNull(val, str);",
+                        "    Objects.requireNonNull(val, \"foo\");",
+                        "    Objects.requireNonNull(val, \"foo\" + \"bar\");",
+                        "    // BUG: Diagnostic contains:",
+                        "    Objects.requireNonNull(val, \"foo \" + val);",
+                        "  }",
+                        "}")
+                .doTest();
+    }
+}

errorprone/tests/res/android/util/Preconditions.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.util;
+
+public class Preconditions {
+    public static void checkArgument(boolean expression) {
+        throw new UnsupportedOperationException();
+    }
+
+    public static void checkArgument(boolean expression, Object errorMessage) {
+        throw new UnsupportedOperationException();
+    }
+
+    public static <T> T checkNotNull(T reference) {
+        throw new UnsupportedOperationException();
+    }
+
+    public static <T> T checkNotNull(T reference, Object errorMessage) {
+        throw new UnsupportedOperationException();
+    }
+
+    public static void checkState(boolean expression) {
+        throw new UnsupportedOperationException();
+    }
+
+    public static void checkState(boolean expression, String message) {
+        throw new UnsupportedOperationException();
+    }
+}