apache工具类之HashCodeBuilder

前言

apache.commons工具类HashCodeBuilder，用于生成对象hashcode值，使用到的设计模式：建造者模式，其设计思想和jdk中的StringBuilder及StringBuffer是一样的，都是将复杂对象的构建过程逐步分解，最后通过build()方法构建出完整的对象或结果。让业务代码更简洁优雅。

代码片段

public class HashCodeBuilder {
   
    private final int iConstant;

    private int iTotal = 0;

    public HashCodeBuilder() {
        iConstant = 37;
        iTotal = 17;
    }

    public HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber) {
        if (initialNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero initial value");
        }
        if (initialNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd initial value");
        }
        if (multiplierNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero multiplier");
        }
        if (multiplierNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd multiplier");
        }
        iConstant = multiplierNonZeroOddNumber;
        iTotal = initialNonZeroOddNumber;
    }
    
    public HashCodeBuilder append(boolean value) {
        iTotal = iTotal * iConstant + (value ? 0 : 1);
        return this;
    }

    public HashCodeBuilder append(boolean[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(byte value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    public HashCodeBuilder append(byte[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(char value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    public HashCodeBuilder append(char[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }
    
    public HashCodeBuilder append(float value) {
        iTotal = iTotal * iConstant + Float.floatToIntBits(value);
        return this;
    }

    public HashCodeBuilder append(float[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(double value) {
        return append(Double.doubleToLongBits(value));
    }

    public HashCodeBuilder append(double[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(short value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    public HashCodeBuilder append(short[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(int value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    public HashCodeBuilder append(int[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(long value) {
        iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
        return this;
    }

    public HashCodeBuilder append(long[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder append(Object object) {
        if (object == null) {
            iTotal = iTotal * iConstant;
        } else {
            if (object.getClass().isArray() == false) {
                // the simple case, not an array, just the element
                iTotal = iTotal * iConstant + object.hashCode();
            } else {
                 // 'Switch' on type of array, to dispatch to the correct handler
                // This handles multi dimensional arrays
                if (object instanceof long[]) {
                    append((long[]) object);
                } else if (object instanceof int[]) {
                    append((int[]) object);
                } else if (object instanceof short[]) {
                    append((short[]) object);
                } else if (object instanceof char[]) {
                    append((char[]) object);
                } else if (object instanceof byte[]) {
                    append((byte[]) object);
                } else if (object instanceof double[]) {
                    append((double[]) object);
                } else if (object instanceof float[]) {
                    append((float[]) object);
                } else if (object instanceof boolean[]) {
                    append((boolean[]) object);
                } else {
                    // Not an array of primitives
                    append((Object[]) object);
                }
            }
        }
        return this;
    }

    public HashCodeBuilder append(Object[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    public HashCodeBuilder appendSuper(int superHashCode) {
        iTotal = iTotal * iConstant + superHashCode;
        return this;
    }

    public int toHashCode() {
        return iTotal;
    }

}

使用示例

public class Person {
   String name;
   int age;
   boolean smoker;
   ...
   
   @Override
   public boolean equals(Object p){
      //重写equals方法
   }
 
   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();
   }
}