All Implemented Interfaces:

external.org.apache.commons.lang3.builder.Builder
```
public class HashCodeBuilder
 implements Builder<Integer>
                    
```
Assists in implementing hashCode methods.
This class enables a good hashCode method to be built for any class. It follows the rules laid out in the book Effective Java by Joshua Bloch. Writing a good hashCode method is actually quite difficult. This class aims to simplify the process.
The following is the approach taken. When appending a data field, the current total is multiplied by the multiplier then a relevant value for that data type is added. For example, if the current hashCode is 17, and the multiplier is 37, then appending the integer 45 will create a hashcode of 674, namely 17 * 37 + 45.
All relevant fields from the object should be included in the hashCode method. Derived fields may be excluded. In general, any field used in the equals method must be used in the hashCodemethod.
To use this class write code as follows:
```
public class Person {
  String name;
  int age;
  boolean smoker;
  ...

  public int hashCode() {
    // you pick a hard-coded, randomly chosen, non-zero, odd number
    // ideally different for each class
    return new HashCodeBuilder(17, 37).
      append(name).
      append(age).
      append(smoker).
      toHashCode();
  }
}
```
If required, the superclass hashCode() can be added using appendSuper.
Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are usually private, the method, reflectionHashCode, uses AccessibleObject.setAccessibleto change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions are set up correctly. It is also slower than testing explicitly.
A typical invocation for this method would look like:
```
public int hashCode() {
  return HashCodeBuilder.reflectionHashCode(this);
}
```

Constructor Summary

Constructors
Constructor	Description
`HashCodeBuilder()`	Uses two hard coded choices for the constants needed to build a `hashCode`.
`HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber)`	Two randomly chosen, non-zero, odd numbers must be passed in.

Method Summary

Modifier and Type	Method	Description
`static int`	`reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object)`	This method uses reflection to build a valid hash code.
`static int`	`reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object, boolean testTransients)`	This method uses reflection to build a valid hash code.
`static <T> int`	`reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, T object, boolean testTransients, Class<out Object> reflectUpToClass, Array<String> excludeFields)`	This method uses reflection to build a valid hash code.
`static int`	`reflectionHashCode(Object object, boolean testTransients)`	This method uses reflection to build a valid hash code.
`static int`	`reflectionHashCode(Object object, Collection<String> excludeFields)`	This method uses reflection to build a valid hash code.
`static int`	`reflectionHashCode(Object object, Array<String> excludeFields)`	This method uses reflection to build a valid hash code.
`HashCodeBuilder`	`append(boolean value)`	Append a `hashCode` for a `boolean`.
`HashCodeBuilder`	`append(Array<boolean> array)`	Append a `hashCode` for a `boolean` array.
`HashCodeBuilder`	`append(byte value)`	Append a `hashCode` for a `byte`.
`HashCodeBuilder`	`append(Array<byte> array)`	Append a `hashCode` for a `byte` array.
`HashCodeBuilder`	`append(char value)`	Append a `hashCode` for a `char`.
`HashCodeBuilder`	`append(Array<char> array)`	Append a `hashCode` for a `char` array.
`HashCodeBuilder`	`append(double value)`	Append a `hashCode` for a `double`.
`HashCodeBuilder`	`append(Array<double> array)`	Append a `hashCode` for a `double` array.
`HashCodeBuilder`	`append(float value)`	Append a `hashCode` for a `float`.
`HashCodeBuilder`	`append(Array<float> array)`	Append a `hashCode` for a `float` array.
`HashCodeBuilder`	`append(int value)`	Append a `hashCode` for an `int`.
`HashCodeBuilder`	`append(Array<int> array)`	Append a `hashCode` for an `int` array.
`HashCodeBuilder`	`append(long value)`	Append a `hashCode` for a `long`.
`HashCodeBuilder`	`append(Array<long> array)`	Append a `hashCode` for a `long` array.
`HashCodeBuilder`	`append(Object object)`	Append a `hashCode` for an `Object`.
`HashCodeBuilder`	`append(Array<Object> array)`	Append a `hashCode` for an `Object` array.
`HashCodeBuilder`	`append(short value)`	Append a `hashCode` for a `short`.
`HashCodeBuilder`	`append(Array<short> array)`	Append a `hashCode` for a `short` array.
`HashCodeBuilder`	`appendSuper(int superHashCode)`	Adds the result of super.hashCode() to this builder.
`int`	`toHashCode()`	Return the computed `hashCode`.
`Integer`	`build()`	Returns the computed `hashCode`.
`int`	`hashCode()`	The computed `hashCode` from toHashCode() is returned due to the likelihoodof bugs in mis-calling toHashCode() and the unlikeliness of it mattering what the hashCode forHashCodeBuilder itself is.

Methods inherited from class external.org.apache.commons.lang3.builder.Builder
build
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - HashCodeBuilder
```
HashCodeBuilder()
```
    Uses two hard coded choices for the constants needed to build a hashCode.
  - HashCodeBuilder
```
HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber)
```
    Two randomly chosen, non-zero, odd numbers must be passed in.
    
    Parameters:
    
    initialNonZeroOddNumber - a non-zero, odd number used as the initial value
    
    multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
- Method Detail
  - reflectionHashCode
```
 static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object)
```
    This method uses reflection to build a valid hash code.
    It uses AccessibleObject.setAccessible to gain access to private fields. This means that it willthrow a security exception if run under a security manager, if the permissions are not set up correctly. It isalso not as efficient as testing explicitly.
    Transient members will be not be used, as they are likely derived fields, and not part of the value of theObject.
    Static fields will not be tested. Superclass fields will be included.
    Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,however this is not vital. Prime numbers are preferred, especially for the multiplier.
    
    Parameters:
    
    initialNonZeroOddNumber - a non-zero, odd number used as the initial value
    
    multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
    
    object - the Object to create a hashCode for
  - reflectionHashCode
```
 static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object, boolean testTransients)
```
    This method uses reflection to build a valid hash code.
    It uses AccessibleObject.setAccessible to gain access to private fields. This means that it willthrow a security exception if run under a security manager, if the permissions are not set up correctly. It isalso not as efficient as testing explicitly.
    If the TestTransients parameter is set to true, transient members will be tested, otherwise theyare ignored, as they are likely derived fields, and not part of the value of the Object.
    Static fields will not be tested. Superclass fields will be included.
    Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,however this is not vital. Prime numbers are preferred, especially for the multiplier.
    
    Parameters:
    
    initialNonZeroOddNumber - a non-zero, odd number used as the initial value
    
    multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
    
    object - the Object to create a hashCode for
    
    testTransients - whether to include transient fields
  - reflectionHashCode
```
 static <T> int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, T object, boolean testTransients, Class<out Object> reflectUpToClass, Array<String> excludeFields)
```
    This method uses reflection to build a valid hash code.
    It uses AccessibleObject.setAccessible to gain access to private fields. This means that it willthrow a security exception if run under a security manager, if the permissions are not set up correctly. It isalso not as efficient as testing explicitly.
    If the TestTransients parameter is set to true, transient members will be tested, otherwise theyare ignored, as they are likely derived fields, and not part of the value of the Object.
    Static fields will not be included. Superclass fields will be included up to and including the specifiedsuperclass. A null superclass is treated as java.lang.Object.
    Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,however this is not vital. Prime numbers are preferred, especially for the multiplier.
    
    Parameters:
    
    initialNonZeroOddNumber - a non-zero, odd number used as the initial value
    
    multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
    
    object - the Object to create a hashCode for
    
    testTransients - whether to include transient fields
    
    reflectUpToClass - the superclass to reflect up to (inclusive), may be null
    
    excludeFields - array of field names to exclude from use in calculation of hash code
  - reflectionHashCode
```
 static int reflectionHashCode(Object object, boolean testTransients)
```
    This method uses reflection to build a valid hash code.
    This constructor uses two hard coded choices for the constants needed to build a hash code.
    It uses AccessibleObject.setAccessible to gain access to private fields. This means that it willthrow a security exception if run under a security manager, if the permissions are not set up correctly. It isalso not as efficient as testing explicitly.
    If the TestTransients parameter is set to true, transient members will be tested, otherwise theyare ignored, as they are likely derived fields, and not part of the value of the Object.
    Static fields will not be tested. Superclass fields will be included.
    
    Parameters:
    
    object - the Object to create a hashCode for
    
    testTransients - whether to include transient fields
  - reflectionHashCode
```
 static int reflectionHashCode(Object object, Collection<String> excludeFields)
```
    This method uses reflection to build a valid hash code.
    This constructor uses two hard coded choices for the constants needed to build a hash code.
    It uses AccessibleObject.setAccessible to gain access to private fields. This means that it willthrow a security exception if run under a security manager, if the permissions are not set up correctly. It isalso not as efficient as testing explicitly.
    Transient members will be not be used, as they are likely derived fields, and not part of the value of theObject.
    Static fields will not be tested. Superclass fields will be included.
    
    Parameters:
    
    object - the Object to create a hashCode for
    
    excludeFields - Collection of String field names to exclude from use in calculation of hash code
  - reflectionHashCode
```
 static int reflectionHashCode(Object object, Array<String> excludeFields)
```
    This method uses reflection to build a valid hash code.
    This constructor uses two hard coded choices for the constants needed to build a hash code.
    It uses AccessibleObject.setAccessible to gain access to private fields. This means that it willthrow a security exception if run under a security manager, if the permissions are not set up correctly. It isalso not as efficient as testing explicitly.
    Transient members will be not be used, as they are likely derived fields, and not part of the value of theObject.
    Static fields will not be tested. Superclass fields will be included.
    
    Parameters:
    
    object - the Object to create a hashCode for
    
    excludeFields - array of field names to exclude from use in calculation of hash code
  - append
```
 HashCodeBuilder append(boolean value)
```
    Append a hashCode for a boolean.
    This adds 1 when true, and 0 when false to the hashCode.
    This is in contrast to the standard java.lang.Boolean.hashCode handling, which computesa hashCode value of 1231 for java.lang.Boolean instancesthat represent true or 1237 for java.lang.Boolean instancesthat represent false.
    This is in accordance with the Effective Java design.
    
    Parameters:
    
    value - the boolean to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<boolean> array)
```
    Append a hashCode for a boolean array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(byte value)
```
    Append a hashCode for a byte.
    
    Parameters:
    
    value - the byte to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<byte> array)
```
    Append a hashCode for a byte array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(char value)
```
    Append a hashCode for a char.
    
    Parameters:
    
    value - the char to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<char> array)
```
    Append a hashCode for a char array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(double value)
```
    Append a hashCode for a double.
    
    Parameters:
    
    value - the double to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<double> array)
```
    Append a hashCode for a double array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(float value)
```
    Append a hashCode for a float.
    
    Parameters:
    
    value - the float to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<float> array)
```
    Append a hashCode for a float array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(int value)
```
    Append a hashCode for an int.
    
    Parameters:
    
    value - the int to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<int> array)
```
    Append a hashCode for an int array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(long value)
```
    Append a hashCode for a long.
    
    Parameters:
    
    value - the long to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<long> array)
```
    Append a hashCode for a long array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(Object object)
```
    Append a hashCode for an Object.
    
    Parameters:
    
    object - the Object to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<Object> array)
```
    Append a hashCode for an Object array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - append
```
 HashCodeBuilder append(short value)
```
    Append a hashCode for a short.
    
    Parameters:
    
    value - the short to add to the hashCode
  - append
```
 HashCodeBuilder append(Array<short> array)
```
    Append a hashCode for a short array.
    
    Parameters:
    
    array - the array to add to the hashCode
  - appendSuper
```
 HashCodeBuilder appendSuper(int superHashCode)
```
    Adds the result of super.hashCode() to this builder.
    
    Parameters:
    
    superHashCode - the result of calling super.hashCode()
  - toHashCode
```
 int toHashCode()
```
    Return the computed hashCode.
  - build
```
 Integer build()
```
    Returns the computed hashCode.
  - hashCode
```
 int hashCode()
```
    The computed hashCode from toHashCode() is returned due to the likelihoodof bugs in mis-calling toHashCode() and the unlikeliness of it mattering what the hashCode forHashCodeBuilder itself is.

Class HashCodeBuilder

Constructor Summary

Method Summary

Methods inherited from class external.org.apache.commons.lang3.builder.Builder

Methods inherited from class java.lang.Object

Constructor Detail

HashCodeBuilder

HashCodeBuilder

Method Detail

reflectionHashCode

reflectionHashCode

reflectionHashCode

reflectionHashCode

reflectionHashCode

reflectionHashCode

append

append

append

append

append

append

append

append

append

append

append

append

append

append

append

append

append

append

appendSuper

toHashCode

build

hashCode