通常情况下，我们需要去推断一个字符串变量是否为空，今天，我特意做了一个小测试
StringUtils.java:
package com.yx.equipment_collection.utils; import android.annotation.SuppressLint;
import android.text.TextUtils;
import android.util.Log; /**
*
* 此类描写叙述的是: 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)); } }
測试为空例如以下：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);
}
測试结果输入例如以下图：
由此图能够看出方法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
測试非空例如以下：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);
}
測试结果例如以下图：
watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQveWFuZ194aW5nXw==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center">
如上图所看到的，首先是方法33(str != null && str != "")比較占优势。方法11(str != null && str.length() > 0)和方法22(str != null && !str.isEmpty())整体来说。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‘==’推断字符串不准确，应该用‘equals’，个人认为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，查看源代码原来isEmpty()已经推断了‘==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;
}
源代码还用于.length()推断，假设你想‘==’不靠谱。推荐使用.length()对于推理方法！
不是单纯的个人意见......谢谢