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      1 /*
      2  * Copyright (C) 2007 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.dexgen.util;
     18 
     19 /**
     20  * Very simple base class that implements a flag to control the mutability
     21  * of instances. This class just provides the flag and a utility to check
     22  * and throw the right exception, but it is up to subclasses to place calls
     23  * to the checker in all the right places.
     24  */
     25 public class MutabilityControl {
     26     /** whether this instance is mutable */
     27     private boolean mutable;
     28 
     29     /**
     30      * Constructs an instance. It is initially mutable.
     31      */
     32     public MutabilityControl() {
     33         mutable = true;
     34     }
     35 
     36     /**
     37      * Constructs an instance, explicitly indicating the mutability.
     38      *
     39      * @param mutable {@code true} iff this instance is mutable
     40      */
     41     public MutabilityControl(boolean mutable) {
     42         this.mutable = mutable;
     43     }
     44 
     45     /**
     46      * Makes this instance immutable.
     47      */
     48     public void setImmutable() {
     49         mutable = false;
     50     }
     51 
     52     /**
     53      * Checks to see whether or not this instance is immutable. This is the
     54      * same as calling {@code !isMutable()}.
     55      *
     56      * @return {@code true} iff this instance is immutable
     57      */
     58     public final boolean isImmutable() {
     59         return !mutable;
     60     }
     61 
     62     /**
     63      * Checks to see whether or not this instance is mutable.
     64      *
     65      * @return {@code true} iff this instance is mutable
     66      */
     67     public final boolean isMutable() {
     68         return mutable;
     69     }
     70 
     71     /**
     72      * Throws {@link MutabilityException} if this instance is
     73      * immutable.
     74      */
     75     public final void throwIfImmutable() {
     76         if (!mutable) {
     77             throw new MutabilityException("immutable instance");
     78         }
     79     }
     80 
     81     /**
     82      * Throws {@link MutabilityException} if this instance is mutable.
     83      */
     84     public final void throwIfMutable() {
     85         if (mutable) {
     86             throw new MutabilityException("mutable instance");
     87         }
     88     }
     89 }
     90