length()代替equals()检验字符串是否为空串

主题
永远也不要使用string.equals(“”)检验一个字符串是空串
最优方案
检验字符串是空串的最好方法是：用length(),这个方法返回字符串中字符的个数，如果字符的个数是0，一定是空串。

public boolean isEmpty(String str){    return str.equals("");        //NEVER do this}public boolean isEmpty(String str){    return str.length()==0;        //Correct way to check empty}

论证
String部分源码如下
length()

public int length() {    return count;}

equals()方法源码

/**     * Compares this string to the specified object.  The result is {@code     * true} if and only if the argument is not {@code null} and is a {@code     * String} object that represents the same sequence of characters as this     * object.     *     * @param  anObject     *         The object to compare this {@code String} against     *     * @return  {@code true} if the given object represents a {@code String}     *          equivalent to this string, {@code false} otherwise     *     * @see  #compareTo(String)     * @see  #equalsIgnoreCase(String)     */    public boolean equals(Object anObject) {        if (this == anObject) {            return true;        }        if (anObject instanceof String) {            String anotherString = (String) anObject;            int n = value.length;            if (n == anotherString.value.length) {                char v1[] = value;                char v2[] = anotherString.value;                int i = 0;                while (n-- != 0) {                    if (v1[i] != v2[i])                            return false;                    i++;                }                return true;            }        }        return false;    }

可以看出length()简单的返回字符的个数，不会浪费太多的CPU,但是equals()方法有很多的判断语句，还创建了临时数组和采用了循环，浪费了大量的CPU资源

java 6以后提供了 isEmpty()方法使用，所以以后用这个方法

/**     * Returns <tt>true</tt> if, and only if, {@link #length()} is <tt>0</tt>.     *     * @return <tt>true</tt> if {@link #length()} is <tt>0</tt>, otherwise     * <tt>false</tt>     *     * @since 1.6     */    public boolean isEmpty() {        return value.length == 0;    }

参考内容：click here