NoCloneCheck.java

////////////////////////////////////////////////////////////////////////////////

// checkstyle: Checks Java source code for adherence to a set of rules.

// Copyright (C) 2001-2018 the original author or authors.

//

// This library is free software; you can redistribute it and/or

// modify it under the terms of the GNU Lesser General Public

// License as published by the Free Software Foundation; either

// version 2.1 of the License, or (at your option) any later version.

//

// This library 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

// Lesser General Public License for more details.

//

// You should have received a copy of the GNU Lesser General Public

// License along with this library; if not, write to the Free Software

// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

////////////////////////////////////////////////////////////////////////////////

package com.puppycrawl.tools.checkstyle.checks.coding;

import com.puppycrawl.tools.checkstyle.StatelessCheck;

import com.puppycrawl.tools.checkstyle.api.AbstractCheck;

import com.puppycrawl.tools.checkstyle.api.DetailAST;

import com.puppycrawl.tools.checkstyle.api.TokenTypes;

/**

 * <p>

 * Checks that the clone method is not overridden from the

 * Object class.

 * </p>

 *

 * <p>Rationale: The clone method relies on strange/hard to follow rules that

 * do not work it all situations.  Consequently, it is difficult to

 * override correctly.  Below are some of the rules/reasons why the clone

 * method should be avoided.

 *

 * <ul>

 * <li>

 * Classes supporting the clone method should implement the Cloneable

 * interface but the Cloneable interface does not include the clone method.

 * As a result, it doesn't enforce the method override.

 * </li>

 * <li>

 * The Cloneable interface forces the Object's clone method to work

 * correctly. Without implementing it, the Object's clone method will

 * throw a CloneNotSupportedException.

 * </li>

 * <li>

 * Non-final classes must return the object returned from a call to

 * super.clone().

 * </li>

 * <li>

 * Final classes can use a constructor to create a clone which is different

 * from non-final classes.

 * </li>

 * <li>

 * If a super class implements the clone method incorrectly all subclasses

 * calling super.clone() are doomed to failure.

 * </li>

 * <li>

 * If a class has references to mutable objects then those object

 * references must be replaced with copies in the clone method

 * after calling super.clone().

 * </li>

 * <li>

 * The clone method does not work correctly with final mutable object

 * references because final references cannot be reassigned.

 * </li>

 * <li>

 * If a super class overrides the clone method then all subclasses must

 * provide a correct clone implementation.

 * </li>

 * </ul>

 *

 * <p>Two alternatives to the clone method, in some cases, is a copy constructor

 * or a static factory method to return copies of an object. Both of these

 * approaches are simpler and do not conflict with final fields. They do not

 * force the calling client to handle a CloneNotSupportedException.  They also

 * are typed therefore no casting is necessary. Finally, they are more

 * flexible since they can take interface types rather than concrete classes.

 *

 * <p>Sometimes a copy constructor or static factory is not an acceptable

 * alternative to the clone method.  The example below highlights the

 * limitation of a copy constructor (or static factory). Assume

 * Square is a subclass for Shape.

 *

 * <pre>

 * Shape s1 = new Square();

 * System.out.println(s1 instanceof Square); //true

 * </pre>

 * ...assume at this point the code knows nothing of s1 being a Square

 *    that's the beauty of polymorphism but the code wants to copy

 *    the Square which is declared as a Shape, its super type...

 *

 * <pre>

 * Shape s2 = new Shape(s1); //using the copy constructor

 * System.out.println(s2 instanceof Square); //false

 * </pre>

 * The working solution (without knowing about all subclasses and doing many

 * casts) is to do the following (assuming correct clone implementation).

 *

 * <pre>

 * Shape s2 = s1.clone();

 * System.out.println(s2 instanceof Square); //true

 * </pre>

 * Just keep in mind if this type of polymorphic cloning is required

 * then a properly implemented clone method may be the best choice.

 *

 * <p>Much of this information was taken from Effective Java:

 * Programming Language Guide First Edition by Joshua Bloch

 * pages 45-52.  Give Bloch credit for writing an excellent book.

 * </p>

 *

 * <p>This check is almost exactly the same as the {@link NoFinalizerCheck}

 *

 * @author Travis Schneeberger

 * @see Object#clone()

 */

@StatelessCheck

    /**

     * A key is pointing to the warning message text in "messages.properties"

     * file.

     */

    public static final String MSG_KEY = "avoid.clone.method";

    @Override

    public int[] getDefaultTokens() {

    }

    @Override

    public int[] getAcceptableTokens() {

    }

    @Override

    public int[] getRequiredTokens() {

    }

    @Override

    public void visitToken(DetailAST aAST) {

            }

        }

}

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