Java中 String.valueOf与toString的差异说明

雨点打透心脏的1/2处 2022-12-27 11:29 141阅读 0赞

在使用对象 转换中，经常能碰到各种类型转换String的需求。

很多同学对于什么时候用String.valueOf，什么时候用toString有点分不清楚。

String.valueOf的代码 如下：

/**
         * Returns the string representation of the {@code Object} argument.
         *
         * @param   obj   an {@code Object}.
         * @return  if the argument is {@code null}, then a string equal to
         *          {@code "null"}; otherwise, the value of
         *          {@code obj.toString()} is returned.
         * @see     java.lang.Object#toString()
         */
        public static String valueOf(Object obj) {
            return (obj == null) ? "null" : obj.toString();
        }

toString源码：

/**
         * Returns a string representation of the object. In general, the
         * {@code toString} method returns a string that
         * "textually represents" this object. The result should
         * be a concise but informative representation that is easy for a
         * person to read.
         * It is recommended that all subclasses override this method.
         * <p>
         * The {@code toString} method for class {@code Object}
         * returns a string consisting of the name of the class of which the
         * object is an instance, the at-sign character `{@code @}', and
         * the unsigned hexadecimal representation of the hash code of the
         * object. In other words, this method returns a string equal to the
         * value of:
         * <blockquote>
         * <pre>
         * getClass().getName() + '@' + Integer.toHexString(hashCode())
         * </pre></blockquote>
         *
         * @return  a string representation of the object.
         */
        public String toString() {
            return getClass().getName() + "@" + Integer.toHexString(hashCode());
        }

String.valueOf对null作了判断。String.valueOf在转换的对象不为空 的时候，则调用 toString()方法 。当对象为null的时候，toString()将报异常：java.lang.NullPointerException。

**总结 ：在使用的时候最好使用String.valueOf方法。**