Three ways to traverse collections in Java

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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