Three traversal methods of java collection ArrayList

ArrayList

ArrayList uses continuous memory units to store data elements and is a dynamic array whose capacity can grow dynamically.

When a data element is added or removed (except for the last position), ArrayList needs to move all elements behind the added (or removed) element. So inserting and deleting elements is slower, and querying is faster.

At the same time, the ArrayList thread is unsafe! Generally, ArrayList is used in single threads, while Vector and CopyOnWriteArrayList are generally used in multi-threads.

Recommended java related video tutorials: java online learning

Note:

1, ArrayList has been covered tostring can print the results directly.

2. toArray() will convert elements into Object type.

ArrayList traversal methods

ArrayList has three traversal methods, namely:

1. Iterator traversal

Iterator<Integer> it = arrayList.iterator();
while(it.hasNext()){
    System.out.print(it.next() + " ");
}

2. Index value traversal

for(int i = 0; i < arrayList.size(); i++){
   System.out.print(arrayList.get(i) + " ");
}

3. for loop traversal

for(Integer number : arrayList){
   System.out.print(number + " ");
}

Note: It should be noted that when traversing ArrayList, traversal through index values ​​is the most efficient, followed by for loop traversal, and iterator traversal is the lowest.

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