如何提高與優化自己的代碼

1. 在for循環下的拼接字符串儘量使用StringBuffer和StringBuilder，這樣可以大大提高運算效率

非提倡：

List<String> list = new ArrayList<String>();

columnNameStr="";

for(String columnName : list) {

columnNameStr+= columnName;

}

提倡：

List<String> list = new ArrayList<String>();

columnNameStr="";

StringBuffer sb = new StringBuffer

for(String columnName : list) {

sb.append(columnName).append(",") ;

}

columnNameStr = sb.toString();

2. 儘量不要在for循環中進行增刪、改、查，最好先結合第一步(1)，然後用XXX = in();

3.對於list集合來說，判斷list集合爲空，list.size()==0和list.isEmpty()的相率相當

@SuppressWarnings("rawtypes")

List list = new ArrayList();

long start = System.currentTimeMillis();

if (list.size() == 0) {

System.out.println("判斷size的效率");

}

long end = System.currentTimeMillis();

System.out.println(end-start); // 0

@SuppressWarnings("rawtypes")

List list = new ArrayList();

long start = System.currentTimeMillis();

if (list.isEmpty()) {

System.out.println("判斷isEmpty的效率");

}

long end = System.currentTimeMillis();

System.out.println(end-start) ;// 0

4.對於字符串採用split()時，如果匹配單字符，最好用str.split(",")而非str.split(str，','),前者的效率更高

long start = System.currentTimeMillis();

String str = "12,e3,4,54,657,8,89,0-=";

String[] strs = str.split(",");

//String[] strs = str.split(str, ',');

long end = System.currentTimeMillis();

System.out.println(end-start) ;// 0

long start = System.currentTimeMillis();

String str = "12,e3,4,54,657,8,89,0-=";

String[] strs = str.split(str, ',');

long end = System.currentTimeMillis();

System.out.println(end-start) ;// 2
5..對於字符串採用indexOf()時，如果匹配單字符，最好用str.indexOf(',')而非str.indexOf(","),lastIndexOf()也有相同情況