這裡我選取作為比較的例子是, 在一個url後面拼接參數。
關于拼接參數, 無非就幾種,一種就是String的 ‘+’ ,一種就是StringBuilder.append(StringBuffer.append) ,還有就是String.format。
先來看看這三種的效果:
TestStringAppend.java
/**
* @Author : JCccc
* @CreateTime : 2019/12/5
* @Description :
**/
public class TestStringAppend {
private static int forTimes=10000;
private static String url = "http://localhost:8080/testSomeThings?";
private static String uId = "100180";
private static String userName = "testName";
private static String userPwd = "Nux321mXJc";
private static void testStringFormat() {
System.out.println("--------------testStringFormat---------------");
long beginTime = System.currentTimeMillis();
String resultStr = String.format("%suId=%s&userName=%s&userPwd=%s", url, uId, userName, userPwd);
System.out.println(resultStr);
System.out.println(System.currentTimeMillis() - beginTime);
}
private static void testStringBuilder() {
System.out.println("--------------testStringBuilder---------------");
long beginTime = System.currentTimeMillis();
StringBuilder resultBuilder = new StringBuilder();
resultBuilder.append(url).append("uId=").append(uId).append("&userName=").append(userName)
.append("&userPwd=").append(userPwd);
String resultStr = resultBuilder.toString();
System.out.println(resultStr);
System.out.println(System.currentTimeMillis() - beginTime);
}
private static void testStringAdd() {
System.out.println("--------------testStringAdd---------------");
long beginTime = System.currentTimeMillis();
String resultStr = url + "uId=" + uId + "&userName=" + userName + "&userPwd=" + userPwd;
System.out.println(resultStr);
System.out.println(System.currentTimeMillis() - beginTime);
}
public static void main(String[] args) {
testStringFormat();
testStringBuilder();
testStringAdd();
}
}
效果:
可以看到,單純一次的拼接下,其實三種方式差異基本可以忽略,沒什麼差別,時間基本可以忽略不計。
接下來我們在每個方法裡面都加入循環,而且加入記憶體占用計算:
private static void testStringFormatFor() {
System.out.println("--------------testStringFormatFor---------------");
Runtime runtime = Runtime.getRuntime();
long memory = runtime.freeMemory();
long beginTime = System.currentTimeMillis();
String resultStr="";
for (int i = 0; i <= forTimes; i++) {
resultStr = String.format("%suId=%s&userName=%s&userPwd=%s", url, uId, userName, userPwd);
}
System.out.println(System.currentTimeMillis() - beginTime);
System.out.println((memory - runtime.freeMemory()) / 10000 + "W");
}
private static void testStringBuilderFor() {
System.out.println("--------------testStringBuilderFor---------------");
Runtime runtime = Runtime.getRuntime();
long memory = runtime.freeMemory();
long beginTime = System.currentTimeMillis();
StringBuilder resultBuilder = new StringBuilder();
for (int i = 0; i <= forTimes; i++) {
resultBuilder.append(url).append("uId=").append(uId).append("&userName=").append(userName)
.append("&userPwd=").append(userPwd);
}
System.out.println(System.currentTimeMillis() - beginTime);
System.out.println((memory - runtime.freeMemory()) / 10000 + "W");
}
private static void testStringAddFor() {
System.out.println("--------------testStringAddFor---------------");
Runtime runtime = Runtime.getRuntime();
long memory = runtime.freeMemory();
long beginTime = System.currentTimeMillis();
String resultStr =null;
for (int i = 0; i <= forTimes; i++) {
resultStr= url + "uId=" + uId + "&userName=" + userName + "&userPwd=" + userPwd;
}
System.out.println(System.currentTimeMillis() - beginTime);
System.out.println((memory - runtime.freeMemory()) / 10000 + "W");
}
這裡循環的次數是 1萬次,這樣就初步差別出差異了:
結論:
StringBuilder 性能最佳,無論在耗時還是耗記憶體方面。
String的 ‘+’ 拼接,性能接近StringBuilder,因為底層其實就是StringBuilder。
String.format 性能最弱,但是如果是單次的拼接上,代碼可讀性最佳。
個人感覺,如果不太注重性能,用String.format是很不錯的,代碼整潔,可讀性很高。
但是實際上用‘+’拼接可讀性也是很高的,為什麼這麼說,因為大部分人都是直接用‘+‘ 拼接,看習慣了可讀性也就提升了。
其次如果需要優化性能,那不用說了,看完這篇你肯定知道怎麼去優化了。