com.google.errorprone.bugpatterns.PrivateConstructorForUtilityClass.java Source code

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Here is the source code for com.google.errorprone.bugpatterns.PrivateConstructorForUtilityClass.java

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/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * 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;

import static com.google.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
import static com.google.errorprone.fixes.SuggestedFixes.addMembers;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.util.ASTHelpers.isGeneratedConstructor;
import static com.sun.source.tree.Tree.Kind.CLASS;
import static com.sun.source.tree.Tree.Kind.METHOD;
import static javax.lang.model.element.Modifier.STATIC;

import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.FluentIterable;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.sun.source.tree.BlockTree;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.VariableTree;

/** @author gak@google.com (Gregory Kick) */
@BugPattern(name = "PrivateConstructorForUtilityClass", summary = "Utility classes (only static members) are not designed to be instantiated and should"
        + " be made noninstantiable with a default constructor.", explanation = "Classes that only include static members have no behavior particular to any given instance,"
                + " so instantiating them is nonsense. To prevent users from mistakenly creating"
                + " instances, the class should include a private constructor.  See Effective Java,"
                + " Second Edition - Item 4.", category = JDK, severity = SUGGESTION)
public final class PrivateConstructorForUtilityClass extends BugChecker implements ClassTreeMatcher {

    @Override
    public Description matchClass(ClassTree classTree, VisitorState state) {
        if (!classTree.getKind().equals(CLASS)) {
            return NO_MATCH;
        }

        FluentIterable<? extends Tree> nonSyntheticMembers = FluentIterable.from(classTree.getMembers())
                .filter(Predicates.not(new Predicate<Tree>() {
                    @Override
                    public boolean apply(Tree tree) {
                        return tree.getKind().equals(METHOD) && isGeneratedConstructor((MethodTree) tree);
                    }
                }));
        if (nonSyntheticMembers.isEmpty()) {
            return NO_MATCH;
        }
        boolean isUtilityClass = nonSyntheticMembers.allMatch(new Predicate<Tree>() {
            @Override
            public boolean apply(Tree tree) {
                switch (tree.getKind()) {
                case CLASS:
                    return ((ClassTree) tree).getModifiers().getFlags().contains(STATIC);
                case METHOD:
                    return ((MethodTree) tree).getModifiers().getFlags().contains(STATIC);
                case VARIABLE:
                    return ((VariableTree) tree).getModifiers().getFlags().contains(STATIC);
                case BLOCK:
                    return ((BlockTree) tree).isStatic();
                case ENUM:
                case ANNOTATION_TYPE:
                case INTERFACE:
                    return true;
                default:
                    throw new AssertionError("unknown member type:" + tree.getKind());
                }
            }
        });
        if (!isUtilityClass) {
            return NO_MATCH;
        }
        return describeMatch(classTree,
                addMembers(classTree, state, "private " + classTree.getSimpleName() + "() {}"));
    }
}