Android比较字符串是否为空(isEmpty)

经常需要判断一个字符串变量是否为空，今天特地做了个小小的测试

StringUtils.java:

package com.yx.equipment_collection.utils;import android.annotation.SuppressLint;import android.text.TextUtils;import android.util.Log;/** *  * 此类描述的是: String帮助类 *  * @author: CS YX * @version:1.0 * @date:2014-10-21 下午2:47:08 */public class StringUtils {private static final String TAG = "StringUtils";private static int count = 100000000;public static void checkEmpty1(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str == null || str.length() < 1) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty1 --- " + (end - start));}@SuppressLint("NewApi")public static void checkEmpty2(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str == null || str.isEmpty()) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty2 --- " + (end - start));}public static void checkEmpty3(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str == null || str == "") {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty3 --- " + (end - start));}public static void checkEmpty4(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str == null || str.equals("")) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty4 --- " + (end - start));}public static void checkEmpty5(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str == null || TextUtils.isEmpty(str)) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty5 --- " + (end - start));}public static void checkEmpty11(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str != null && str.length() > 0) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty11 --- " + (end - start));}@SuppressLint("NewApi")public static void checkEmpty22(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str != null && !str.isEmpty()) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty22 --- " + (end - start));}public static void checkEmpty33(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str != null && str != "") {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty33 --- " + (end - start));}public static void checkEmpty44(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str != null && !str.equals("")) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty44 --- " + (end - start));}public static void checkEmpty55(String str) {long start = System.currentTimeMillis();for (int i = 0; i < count; i++) {if (str != null && !TextUtils.isEmpty(str)) {}}long end = System.currentTimeMillis();Log.i(TAG, "checkEmpty55 --- " + (end - start));}}

测试为空如下：test

public void test() {String str = "";Log.i("test", "str=\"\"---");StringUtils.checkEmpty1(str);StringUtils.checkEmpty2(str);StringUtils.checkEmpty3(str);StringUtils.checkEmpty4(str);StringUtils.checkEmpty5(str);str = null;Log.i("test", "str=null---");StringUtils.checkEmpty1(str);StringUtils.checkEmpty2(str);StringUtils.checkEmpty3(str);StringUtils.checkEmpty4(str);StringUtils.checkEmpty5(str);str = "null";Log.i("test", "str=\"null\"---");StringUtils.checkEmpty1(str);StringUtils.checkEmpty2(str);StringUtils.checkEmpty3(str);StringUtils.checkEmpty4(str);StringUtils.checkEmpty5(str);str = new String();Log.i("test", "str=new String()---");StringUtils.checkEmpty1(str);StringUtils.checkEmpty2(str);StringUtils.checkEmpty3(str);StringUtils.checkEmpty4(str);StringUtils.checkEmpty5(str);}

测试结果输入如下图：

Android比较字符串是否为空(isEmpty)_第1张图片

由此图可以看出方法3(str == "")用时是最少的；其次就是方法1(str.length() < 1)和方法2(str.isEmpty()) ;

方法4(str.equals(""))耗时较多;方法5(TextUtils.isEmpty(str))最耗时

测试非空如下：test

public void test1() {String str = "";Log.i("test", "str=\"\"---");StringUtils.checkEmpty11(str);StringUtils.checkEmpty22(str);StringUtils.checkEmpty33(str);StringUtils.checkEmpty44(str);StringUtils.checkEmpty55(str);str = null;Log.i("test", "str=null---");StringUtils.checkEmpty11(str);StringUtils.checkEmpty22(str);StringUtils.checkEmpty33(str);StringUtils.checkEmpty44(str);StringUtils.checkEmpty55(str);str = "null";Log.i("test", "str=\"null\"---");StringUtils.checkEmpty11(str);StringUtils.checkEmpty22(str);StringUtils.checkEmpty33(str);StringUtils.checkEmpty44(str);StringUtils.checkEmpty55(str);str = new String();Log.i("test", "str=new String()---");StringUtils.checkEmpty11(str);StringUtils.checkEmpty22(str);StringUtils.checkEmpty33(str);StringUtils.checkEmpty44(str);StringUtils.checkEmpty55(str);}

测试结果如下图：

Android比较字符串是否为空(isEmpty)_第2张图片

如上图所示，首先是方法33(str != null && str != "")比较占优势；方法11(str != null && str.length() > 0)和方法22(str != null && !str.isEmpty())总体来说，不相上下；

方法44(str != null && !str.equals(str != null && !TextUtils.isEmpty(str)))较耗时；方法55()还是最耗时

也有人说，用‘==’判断字符串不准确，应该用‘equals’，个人觉得String一般都是直接=定义，想必没有几个人定义一个字符串会new出来吧。

为什么TextUtils.isEmpty()耗时最多，查看源码原来isEmpty()已经判断了‘==null’：

    /**     * Returns true if the string is null or 0-length.     * @param str the string to be examined     * @return true if str is null or zero length     */    public static boolean isEmpty(CharSequence str) {        if (str == null || str.length() == 0)            return true;        else            return false;    }

源码也是用.length()判断的，如果你觉得‘==’不靠谱，推荐使用.length()方法判断！

以上纯属个人见解......谢谢

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