java 哈希码

加入新的元素到数组中

    /**
     * Append the given object to the given array, returning a new array
     * consisting of the input array contents plus the given object.
     * @param array the array to append to (can be {@code null})
     * @param obj the object to append
     * @return the new array (of the same component type; never {@code null})
     */
    public static <A, O extends A> A[] addObjectToArray(A[] array, O obj) {
        Class<?> compType = Object.class;
        if (array != null) {
            compType = array.getClass().getComponentType();
        }
        else if (obj != null) {
            compType = obj.getClass();
        }
        int newArrLength = (array != null ? array.length + 1 : 1);
        @SuppressWarnings("unchecked")
        A[] newArr = (A[]) Array.newInstance(compType, newArrLength);
        if (array != null) {
            System.arraycopy(array, 0, newArr, 0, array.length);
        }
        newArr[newArr.length - 1] = obj;
        return newArr;
    }

把数组转换成Object数组

    /**
     * Convert the given array (which may be a primitive array) to an
     * object array (if necessary of primitive wrapper objects).
     * <p>A {@code null} source value will be converted to an
     * empty Object array.
     * @param source the (potentially primitive) array
     * @return the corresponding object array (never {@code null})
     * @throws IllegalArgumentException if the parameter is not an array
     */
    public static Object[] toObjectArray(Object source) {
        if (source instanceof Object[]) {
            return (Object[]) source;
        }
        if (source == null) {
            return new Object[0];
        }
        if (!source.getClass().isArray()) {
            throw new IllegalArgumentException("Source is not an array: " + source);
        }
        int length = Array.getLength(source);
        if (length == 0) {
            return new Object[0];
        }
        Class<?> wrapperType = Array.get(source, 0).getClass();
        Object[] newArray = (Object[]) Array.newInstance(wrapperType, length);
        for (int i = 0; i < length; i++) {
            newArray[i] = Array.get(source, i);
        }
        return newArray;
    }

返回哈希码

    /**
     * Return as hash code for the given object; typically the value of
     * {@code Object#hashCode()}}. If the object is an array,
     * this method will delegate to any of the {@code nullSafeHashCode}
     * methods for arrays in this class. If the object is {@code null},
     * this method returns 0.
     * @see #nullSafeHashCode(Object[])
     * @see #nullSafeHashCode(boolean[])
     * @see #nullSafeHashCode(byte[])
     * @see #nullSafeHashCode(char[])
     * @see #nullSafeHashCode(double[])
     * @see #nullSafeHashCode(float[])
     * @see #nullSafeHashCode(int[])
     * @see #nullSafeHashCode(long[])
     * @see #nullSafeHashCode(short[])
     */
    public static int nullSafeHashCode(Object obj) {
        if (obj == null) {
            return 0;
        }
        if (obj.getClass().isArray()) {
            if (obj instanceof Object[]) {
                return nullSafeHashCode((Object[]) obj);
            }
            if (obj instanceof boolean[]) {
                return nullSafeHashCode((boolean[]) obj);
            }
            if (obj instanceof byte[]) {
                return nullSafeHashCode((byte[]) obj);
            }
            if (obj instanceof char[]) {
                return nullSafeHashCode((char[]) obj);
            }
            if (obj instanceof double[]) {
                return nullSafeHashCode((double[]) obj);
            }
            if (obj instanceof float[]) {
                return nullSafeHashCode((float[]) obj);
            }
            if (obj instanceof int[]) {
                return nullSafeHashCode((int[]) obj);
            }
            if (obj instanceof long[]) {
                return nullSafeHashCode((long[]) obj);
            }
            if (obj instanceof short[]) {
                return nullSafeHashCode((short[]) obj);
            }
        }
        return obj.hashCode();
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(Object[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (Object element : array) {
            hash = MULTIPLIER * hash + nullSafeHashCode(element);
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(boolean[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (boolean element : array) {
            hash = MULTIPLIER * hash + hashCode(element);
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(byte[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (byte element : array) {
            hash = MULTIPLIER * hash + element;
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(char[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (char element : array) {
            hash = MULTIPLIER * hash + element;
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(double[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (double element : array) {
            hash = MULTIPLIER * hash + hashCode(element);
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(float[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (float element : array) {
            hash = MULTIPLIER * hash + hashCode(element);
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(int[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (int element : array) {
            hash = MULTIPLIER * hash + element;
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(long[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (long element : array) {
            hash = MULTIPLIER * hash + hashCode(element);
        }
        return hash;
    }

    /**
     * Return a hash code based on the contents of the specified array.
     * If {@code array} is {@code null}, this method returns 0.
     */
    public static int nullSafeHashCode(short[] array) {
        if (array == null) {
            return 0;
        }
        int hash = INITIAL_HASH;
        for (short element : array) {
            hash = MULTIPLIER * hash + element;
        }
        return hash;
    }

    /**
     * Return the same value as {@link Boolean#hashCode()}}.
     * @see Boolean#hashCode()
     */
    public static int hashCode(boolean bool) {
        return (bool ? 1231 : 1237);
    }

    /**
     * Return the same value as {@link Double#hashCode()}}.
     * @see Double#hashCode()
     */
    public static int hashCode(double dbl) {
        return hashCode(Double.doubleToLongBits(dbl));
    }

    /**
     * Return the same value as {@link Float#hashCode()}}.
     * @see Float#hashCode()
     */
    public static int hashCode(float flt) {
        return Float.floatToIntBits(flt);
    }

    /**
     * Return the same value as {@link Long#hashCode()}}.
     * @see Long#hashCode()
     */
    public static int hashCode(long lng) {
        return (int) (lng ^ (lng >>> 32));
    }