是否在for循环中使用break？

Question

Just one quick question, say, Car class extends HashMap(String, String).

1.

for (Car car : carList) {
    if (car.isEmpty) {
        break;
    }
    doSomething();
}

2.

for (Car car : carList) {
    if (!car.isEmpty) {
        doSomethingElse();
    }
}

Which of the above two is better? Thanks.

---- edited ---- Sorry I did not make my point clear.

The doSomething() method is actually doing different things. I've changed them to doSomething() and doSometingElse().

My question is, will you put all the process in one if()? or first break the loop if the if() condition does not satisfy.

Thanks.

Answer 1

They do completely different things. The former will stop iterating as soon as the condition is true, whereas the latter will merely skip the processing during the iterations where the condition is false.

Changing the break to continue in the first will make them work the same way.

Answer 2

They do completely different things. First one will stope after seeing first empty car. Second version will 'do something' for each non-empty car. I think, you might want to use continue operator instead of break .

Answer 3

These 2 loops don't do the same thing

1. will terminate the loop the first time it finds an empty car with isEmpty skipping any cars after the first empty one. You can make this work like 2. if you change ' break ' to ' continue '

2. will doSomething for all not-empty cars.

Answer 4

取决于你想要做什么，第一个循环将在条件满足时结束，而第二个循环将遍历所有散列映射。

Answer 5

If you actually meant "continue" and not "break", then I'd say not using continue or break is better.

It's not a huge deal, but statements like continue, break and return are all essentially goto statements that have been dressed up a little. Instead of goto a line or goto a label they goto the top or bottom of a control structure--it makes the programmer have to think a little bit when they track it which means wasted time and additional chances for errors.

It's not a terribly big deal, and many times these structures will actually clarify your code, but if you have a choice and they seem to do essentially the same thing, go the way that doesn't involve sending control elsewhere.

Answer 6

If you want different behavior based on if the car is empty or not, you can use an if else statement. Use break if you want to stop iterating carList.

for (Car car : carList) {
   if (car.isEmpty) {
      doSomething();
   }
   else {
      doSomethingElse();
   }
}

Answer 7

As everyone has pointed out, the break version will exit early. The answer then depends on what you want it to do.

If you've finished doing what you need to do then break out as soon as you're done. Why waste CPU cycles? on the other hand if you must go through the whole list to dosomethingelse() then don't break out.

Were you meant to have two different named functions or should they both be called dosomething() ?

Answer 8

Is this what you're looking for?

for (Car car : carList) {
    if (car.isEmpty) {
         doSomething();
    }
    else {
         doSomethingElse();
    }       
}

Or are you looking for

for (Car car : carList) {
    if (car.isEmpty) {
       break; 
       //STOP ITERATING THROUGH THE REST OF THE LIST 
       //(doSomething & soSomethingElse may have been called a few times already)
    }
    else {
        doSomething();
    }
    doSomethingElse();
}

There are other options as well, your clarification still isn't clear... to me anyway...