com.phloc.commons.hash.HashCodeGenerator Maven / Gradle / Ivy
/**
* Copyright (C) 2006-2015 phloc systems
* http://www.phloc.com
* office[at]phloc[dot]com
*
* 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.phloc.commons.hash;
import java.util.Map;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.NotThreadSafe;
import org.w3c.dom.Node;
import com.phloc.commons.ValueEnforcer;
/**
* A small hash code creation class based on the article found in the net. See
* this article for details.
* After calling {@link #append(Object)} for all objects use
* {@link #getHashCode()} to retrieve the calculated hash code. Once the hash
* code was calculated no modifications are allowed.
*
* A real world example for a final class derived from {@link Object} or a base
* class looks like this: @Override
* public int hashCode () {
* return new HashCodeGenerator (this).append (member1).append (member2).getHashCode ();
* }
*
* For a derived class, the typical code looks like this, assuming the base
* class also uses {@link HashCodeGenerator}: @Override
* public int hashCode () {
* return HashCodeGenerator.getDerived (super.hashCode ()).append (member3).append (member4).getHashCode ();
* }
*
* @author Philip Helger
*/
@NotThreadSafe
public final class HashCodeGenerator implements IHashCodeGenerator
{
/** Use a prime number as the start. */
public static final int INITIAL_HASHCODE = 17;
/**
* Once the hash code generation has been queried, no further changes may be
* done. This flag indicates, whether new items can be added or not.
*/
private boolean m_bClosed = false;
/** The current hash code value. */
private int m_nHC = INITIAL_HASHCODE;
/**
* This is a sanity constructor that allows for any object to be passed in the
* constructor (e.g. this) from which the class is extracted as
* the initial value of the hash code.
*
* @param aSrcObject
* The source object from which the class is extracted. May not be
* null.
*/
public HashCodeGenerator (@Nonnull final Object aSrcObject)
{
this (aSrcObject instanceof Class ? (Class ) aSrcObject : aSrcObject.getClass ());
}
/**
* This constructor requires a class name, because in case a class has no
* instance variables the hash code may be the same for different instances of
* different classes.
*
* @param aClass
* The class this instance is about to create a hash code for. May not
* be null.
*/
public HashCodeGenerator (@Nonnull final Class aClass)
{
ValueEnforcer.notNull (aClass, "Class");
// Use the class name
append (aClass.getName ());
// Is it an array class? If so add the component class name.
final Class aComponentType = aClass.getComponentType ();
if (aComponentType != null)
append (aComponentType.getName ());
}
private HashCodeGenerator (final int nSuperHashCode)
{
m_nHC = nSuperHashCode;
}
private void _checkClosed ()
{
if (m_bClosed)
throw new IllegalStateException ("Hash code cannot be changed anymore!");
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final boolean x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final byte x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final char x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final double x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final float x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final int x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final long x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Atomic type hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (final short x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Object hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Object x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Object hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Enum x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final boolean [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final byte [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final char [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final double [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final float [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final int [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final long [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final short [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Object [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Array hash code generation.
*
* @param x
* Array to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Enum [] x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Type specific hash code generation because parameter class has no
* overloaded equals method.
*
* @param x
* object to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final StringBuffer x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Type specific hash code generation because parameter class has no
* overloaded equals method.
*
* @param x
* object to add
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final StringBuilder x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* @param x
* to be included in the hash code generation.
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Iterable x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* @param x
* to be included in the hash code generation.
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Map x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* @param x
* to be included in the hash code generation.
* @return this
*/
@Nonnull
public HashCodeGenerator append (@Nullable final Node x)
{
_checkClosed ();
m_nHC = HashCodeCalculator.append (m_nHC, x);
return this;
}
/**
* Retrieve the final hash code. Once this method has been called, no further
* calls to append can be done since the hash value is locked!
*
* @return The finally completed hash code. The returned value is never
* {@link #ILLEGAL_HASHCODE}. If the calculated hash code would be
* {@link #ILLEGAL_HASHCODE} it is changed to -1 instead.
*/
public int getHashCode ()
{
m_bClosed = true;
// This is for the very rare case, that the calculated hash code results in
// an illegal value.
if (m_nHC == ILLEGAL_HASHCODE)
m_nHC = -1;
return m_nHC;
}
/**
* @return The same as {@link #getHashCode()} but as an {@link Integer}
* object. Never null.
*/
@Nonnull
public Integer getHashCodeObj ()
{
return Integer.valueOf (getHashCode ());
}
/**
* Never compare {@link HashCodeGenerator} objects :)
*/
@Deprecated
@Override
public boolean equals (final Object o)
{
return o == this;
}
/**
* Always use {@link #getHashCode()}
*
* @return {@link #getHashCode()}
* @see #getHashCode()
*/
@Override
@Deprecated
public int hashCode ()
{
return getHashCode ();
}
/**
* Create a {@link HashCodeGenerator} for derived classes where the base class
* also uses the {@link HashCodeGenerator}. This avoid calculating the hash
* code of the class name more than once.
*
* @param nSuperHashCode
* Always pass in super.hashCode ()
* @return Never null
*/
@Nonnull
public static HashCodeGenerator getDerived (final int nSuperHashCode)
{
if (nSuperHashCode == ILLEGAL_HASHCODE)
throw new IllegalArgumentException ("Passed hash code is invalid!");
return new HashCodeGenerator (nSuperHashCode);
}
}