java程序中比较常见的四种判断是否为空的性能优化比较
来做个测试
java用的最多的判空，殊不知，多数人一直在用一种最耗时，性能最差的方式
本测试用例特意比较常用的4种判空形式
/**
* 字符串判空性能大比较
*/
public class Test{
String s = "";
long n = 10000000;
//s == null || s.equals("")
private void function1(){
long startTime = System.currentTimeMillis();
for (long i = 0; i < n; i++){
if (s == null || s.equals(""))
;
}
long endTime = System.currentTimeMillis();
System.out.println("[s == null || s.equals(\"\")] use time: " + (endTime - startTime) + "ms");
}
//s == null || s.length() <= 0
private void function2(){
long startTime = System.currentTimeMillis();
for (long i = 0; i < n; i++){
if (s == null || s.length() <= 0)
;
}
long endTime = System.currentTimeMillis();
System.out.println("[s == null || s.length() <= 0] use time: " + (endTime - startTime) + "ms");
}
//s == null || s.isEmpty()
private void function3(){
long startTime = System.currentTimeMillis();
for (long i = 0; i < n; i++){
if (s == null || s.isEmpty())//since jdk1.6
;
}
long endTime = System.currentTimeMillis();
System.out.println("[s == null || s.isEmpty()] use time: " + (endTime - startTime) + "ms");
}
//s == null || s == ""
private void function4(){
long startTime = System.currentTimeMillis();
for (long i = 0; i < n; i++){
if (s == null || s == "")
;
}
long endTime = System.currentTimeMillis();
System.out.println("[s == null || s == \"\"] use time: " + (endTime - startTime) + "ms");
}
public static void main(String[] args){
Test test = new Test();
test.function1();
test.function2();
test.function3();
test.function4();
}
}
直接右键运行，结果一目了然
[s == null || s.equals("")] use time: 73ms
[s == null || s.length() <= 0] use time: 29ms
[s == null || s.isEmpty()] use time: 33ms
[s == null || s == ""] use time: 29ms
以下是java 判断字符串是否为空的四种方法:
方法一: 最多人使用的一个方法, 直观, 方便, 但效率很低:
if(s == null ||"".equals(s));
方法二: 比较字符串长度, 效率高, 是我知道的最好一个方法:
if(s == null || s.length() <= 0);
方法三: Java SE 6.0 才开始提供的方法, 效率和方法二几乎相等, 但出于兼容性考虑, 推荐使用方法二.
if(s == null || s.isEmpty());
方法四: 这是一种比较直观,简便的方法,而且效率也非常的高,与方法二、三的效率差不多:
if (s == null || s == "");
public class Zifuchuanpankong {
public static final String STR = "1111111";
public static void function1(){
long startTime = System.currentTimeMillis();
for (int i = 0; i < 10000000; i++) {
if (STR == null || "".equals(STR)) {
;
}
}
long endTime = System.currentTimeMillis();
System.err.println("[STR == null || \"\".equals(STR)] 耗时："+(endTime-startTime)+" ms");
}
public static void function2(){
long startTime = System.currentTimeMillis();
for (int i = 0; i < 10000000; i++) {
if (STR == null || STR.length()<=0) {
;
}
}
long endTime = System.currentTimeMillis();
System.err.println("[STR == null || STR.length()<=0] 耗时："+(endTime-startTime)+" ms");
}
public static void function3(){
long startTime = System.currentTimeMillis();
for (int i = 0; i < 10000000; i++) {
if (STR == null || STR.isEmpty()) {
;
}
}
long endTime = System.currentTimeMillis();
System.err.println("[STR == null || STR.isEmpty()] 耗时："+(endTime-startTime)+" ms");
}
public static void function4(){
long startTime = System.currentTimeMillis();
for (int i = 0; i < 10000000; i++) {
if (STR == null || STR == "") {
;
}
}
long endTime = System.currentTimeMillis();
System.err.println("[STR == null || STR == \"\"] 耗时："+(endTime-startTime)+" ms");
}
public static void main(String[] args) {
function1();
function2();
function3();
function4();
}
}[STR == null || "".equals(STR)] 耗时：51 ms
[STR == null || STR.length()<=0] 耗时：7 ms
[STR == null || STR.isEmpty()] 耗时：9 ms
[STR == null || STR == ""] 耗时：4 ms
