for-each vs for vs while [英] for-each vs for vs while
问题描述
我想知道在ArrayList或每种List上实现"for-each"循环的最佳方法是什么.
I wonder what is the best way to implement a "for-each" loop over an ArrayList or every kind of List.
以下哪种实现是最好的，为什么?还是有最好的方法?
Which of the followings implementations is the best and why? Or is there a best way?
谢谢您的帮助.
List values = new ArrayList();values.add("one"); values.add("two"); values.add("three"); ...
values.add("one"); values.add("two"); values.add("three"); ...
//#0
for(String value : values) {
...
}
//#0
for(String value : values) {
...
}
//#1
for(int i = 0; i < values.size(); i++) {
String value = values.get(i);
...
}
//#1
for(int i = 0; i < values.size(); i++) {
String value = values.get(i);
...
}
//#2
for(Iterator it = values.iterator(); it.hasNext(); ) {
String value = it.next();
...
}
//#2
for(Iterator it = values.iterator(); it.hasNext(); ) {
String value = it.next();
...
}
//#3
Iterator it = values.iterator();
while (it.hasNext()) {
String value = (String) it.next();
...
}
//#3
Iterator it = values.iterator();
while (it.hasNext()) {
String value = (String) it.next();
...
}
推荐答案
#3有一个缺点，因为迭代器it的范围超出了循环的结尾.其他解决方案没有这个问题.
#3 has a disadvantage because the scope of the iterator it extends beyond the end of the loop. The other solutions don't have this problem.
#2与#0完全相同，只是#0更具可读性且不易出错.
#2 is exactly the same as #0, except #0 is more readable and less prone to error.
#1的效率(可能)较低，因为它每次在循环中都会调用.size().
#1 is (probably) less efficient because it calls .size() every time through the loop.
#0通常是最好的，因为:
#0 is usually best because:
- 它是最短的
- 最不容易出错
- 其他人一目了然，很容易理解
- 由编译器有效地实现
- 它不会使用不必要的名称污染您的方法范围(循环外)
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