java toString方法

    //---------------------------------------------------------------------
    // Convenience methods for toString output
    //---------------------------------------------------------------------

    /**
     * Return a String representation of an object‘s overall identity.
     * @param obj the object (may be {@code null})
     * @return the object‘s identity as String representation,
     * or an empty String if the object was {@code null}
     */
    public static String identityToString(Object obj) {
        if (obj == null) {
            return EMPTY_STRING;
        }
        return obj.getClass().getName() + "@" + getIdentityHexString(obj);
    }

    /**
     * Return a hex String form of an object‘s identity hash code.
     * @param obj the object
     * @return the object‘s identity code in hex notation
     */
    public static String getIdentityHexString(Object obj) {
        return Integer.toHexString(System.identityHashCode(obj));
    }

    /**
     * Return a content-based String representation if {@code obj} is
     * not {@code null}; otherwise returns an empty String.
     * <p>Differs from {@link #nullSafeToString(Object)} in that it returns
     * an empty String rather than "null" for a {@code null} value.
     * @param obj the object to build a display String for
     * @return a display String representation of {@code obj}
     * @see #nullSafeToString(Object)
     */
    public static String getDisplayString(Object obj) {
        if (obj == null) {
            return EMPTY_STRING;
        }
        return nullSafeToString(obj);
    }

    /**
     * Determine the class name for the given object.
     * <p>Returns {@code "null"} if {@code obj} is {@code null}.
     * @param obj the object to introspect (may be {@code null})
     * @return the corresponding class name
     */
    public static String nullSafeClassName(Object obj) {
        return (obj != null ? obj.getClass().getName() : NULL_STRING);
    }

    /**
     * Return a String representation of the specified Object.
     * <p>Builds a String representation of the contents in case of an array.
     * Returns {@code "null"} if {@code obj} is {@code null}.
     * @param obj the object to build a String representation for
     * @return a String representation of {@code obj}
     */
    public static String nullSafeToString(Object obj) {
        if (obj == null) {
            return NULL_STRING;
        }
        if (obj instanceof String) {
            return (String) obj;
        }
        if (obj instanceof Object[]) {
            return nullSafeToString((Object[]) obj);
        }
        if (obj instanceof boolean[]) {
            return nullSafeToString((boolean[]) obj);
        }
        if (obj instanceof byte[]) {
            return nullSafeToString((byte[]) obj);
        }
        if (obj instanceof char[]) {
            return nullSafeToString((char[]) obj);
        }
        if (obj instanceof double[]) {
            return nullSafeToString((double[]) obj);
        }
        if (obj instanceof float[]) {
            return nullSafeToString((float[]) obj);
        }
        if (obj instanceof int[]) {
            return nullSafeToString((int[]) obj);
        }
        if (obj instanceof long[]) {
            return nullSafeToString((long[]) obj);
        }
        if (obj instanceof short[]) {
            return nullSafeToString((short[]) obj);
        }
        String str = obj.toString();
        return (str != null ? str : EMPTY_STRING);
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(Object[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }
            sb.append(String.valueOf(array[i]));
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(boolean[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }

            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(byte[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }
            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(char[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }
            sb.append("‘").append(array[i]).append("‘");
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(double[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }

            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(float[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }

            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(int[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }
            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(long[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }
            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }

    /**
     * Return a String representation of the contents of the specified array.
     * <p>The String representation consists of a list of the array‘s elements,
     * enclosed in curly braces ({@code "{}"}). Adjacent elements are separated
     * by the characters {@code ", "} (a comma followed by a space). Returns
     * {@code "null"} if {@code array} is {@code null}.
     * @param array the array to build a String representation for
     * @return a String representation of {@code array}
     */
    public static String nullSafeToString(short[] array) {
        if (array == null) {
            return NULL_STRING;
        }
        int length = array.length;
        if (length == 0) {
            return EMPTY_ARRAY;
        }
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            if (i == 0) {
                sb.append(ARRAY_START);
            }
            else {
                sb.append(ARRAY_ELEMENT_SEPARATOR);
            }
            sb.append(array[i]);
        }
        sb.append(ARRAY_END);
        return sb.toString();
    }