For traversing a collection to obtain its objects, here are three simple ways to summarize it
Method 1: Turn the collection into an array, and then traverse the array
Object[] obj = list.toArray(); for(Object s : obj){ System.out.println((String) s); }
Method 2: Get() method. But it can only be used in list collections. Only List collections have index values.
for(int i = 0;i<list.size();i++){ System.out.println(list.get(i)); }
Method 3: Through iterator
ListIterator it = list.listIterator(); while(it.hasNext()){ System.out.println(it.next()); }
Here are two cases for comparison
Collection case:
import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.List; public class paseWork { public static void main(String[] args) { CollectionTest(); } public static void CollectionTest(){ Collection <String>collection = new ArrayList<String>(); collection.add("初一"); collection.add("小二"); collection.add("张三"); collection.add("李四"); collection.add("王五"); //1.集合转为数组 Object[] Object[] objectsArrC = collection.toArray(); for (Object object : objectsArrC) { String string = (String) object; // 将对象强制转换为字符串输出 System.out.println(string); } //2.get()方法获取元素 for (int i = 0;i < collection.size();i++){ //get()只能用在list集合中,所以这里需要转换形式 System.out.println(((ArrayList<String>) collection).get(i)); } //3.迭代器 Iterator<String> it = collection.iterator(); while(it.hasNext()){ System.out.println(it.next()); } } }
List case:
import java.util.ArrayList; import java.util.Collection; import java.util.List; import java.util.ListIterator; public class paseWork { public static void main(String[] args) { ListTest(); } public static void ListTest(){ List<String> list = new ArrayList<String>(); list.add("初一"); list.add("小二"); list.add("张三"); list.add("李四"); list.add("王五"); //1.集合转为数组 Object[] Object[] objectsArrL = list.toArray(); for (Object object : objectsArrL) { String string = (String) object; //将对象强制转换为字符串输出 System.out.println(string); } //2.通过 get() 方法 for (int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); } //3.迭代器 ListIterator<String> iterator = list.listIterator(); while(iterator.hasNext()){ System.out.println(iterator.next()); } } }
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