在Java中List有三種遍歷方式，1.fori，2.foreach，3.Iterator

List<String> listTest = new ArrayList<>(8);

fori循環(huán)

int size = listTest.size();
for (int i = 0; i < size; i++) {
     System.out.println("fori:"+listTest.get(i));
}

foreach循環(huán)

for (String str:listTest) {
     System.out.println("foreach:"+str);
}

Iterator循環(huán)

Iterator iterator = listTest.iterator();
while (iterator.hasNext()){
    System.out.println("Iterator:"+iterator.next());
}

思考 如何在list的循環(huán)中安全的刪除元素

1.fori中刪除

int size = listTest.size();
for (int i = 0; i < size; i++) {
    System.out.println("fori:" + listTest.get(i));
    listTest.remove(i);
}

java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
    at java.util.ArrayList.rangeCheck(ArrayList.java:657)
    at java.util.ArrayList.get(ArrayList.java:433)

2. foreach中刪除

for (String str : listTest) {
    listTest.remove(str);
    System.out.println("foreach:" + str);
}

java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
    at java.util.ArrayList$Itr.next(ArrayList.java:859)

3. Iterator中刪除

Iterator iterator = listTest.iterator();
while (iterator.hasNext()) {
    System.out.println("Iterator:" + iterator.next());
    iterator.remove();
}

Iterator:a
Iterator:b
Iterator:c
Iterator:d
Iterator:e
Iterator:f
Iterator:g

總結

三種循環(huán)性能上有所差異，但是在遍歷是刪除元素應當使用Iterator迭代器！！

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