[Java知识库]Java优化点总结

1、split切割

数据量过大时可使用StringTokenizer进行处理

两个代码执行差15倍左右

StringBuilder aa = new StringBuilder();
for(int i = 0; i < 1000000; i++){
   aa = aa.append(i).append(",");
}
long begin = System.currentTimeMillis();
aa.toString().split(",");
System.out.println(System.currentTimeMillis() - begin);
begin = System.currentTimeMillis();
new StringTokenizer(aa.toString(), ",");
System.out.println(System.currentTimeMillis() - begin);

2、无需顺序的map，用parallelStream

   List<Demo> aa = new ArrayList<>();
   for(int i = 0; i < 10000000; i++){
       aa.add(getDemo(i));
   }
   long begin = System.currentTimeMillis();
   aa.stream().collect(Collectors.toMap(Demo::getNum, Function.identity()));
   System.out.println(System.currentTimeMillis() - begin);
   begin = System.currentTimeMillis();
   aa.parallelStream().collect(Collectors.toMap(Demo::getNum, Function.identity()));
   System.out.println(System.currentTimeMillis() - begin);