集合与数组的遍历方法

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//map集合遍历方式
public class MapTraversal {
public static void main(String[] args) {
Map<Integer,String> map = new HashMap<Integer, String>();
map.put(1,"岳飞");
map.put(2,"韩世忠");
map.put(3,"杨再兴");
//1.for循环,keySet拿到key取value
for (Integer id : map.keySet()) {
System.out.println(id+"号武将: "+map.get(id));
}
//2.迭代器循环 Iterator
for (Iterator i = map.keySet().iterator();i.hasNext();){
Object o = i.next();
System.out.println(o+"号武将: "+map.get(o));
}
//3.for循环,entrySet拿到键值对
for (Map.Entry<Integer, String> res : map.entrySet()) {
System.out.println(res.getKey()+res.getValue());
}
}
}

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//集合遍历
public class ListTravelsal {
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
//1.for i 索引
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i));
}
//2.for
元素
for (Integer i : list) {
System.out.println(i);
}
//3.迭代器
Iterator<Integer> it = list.iterator();//通过集合对象获取对应的迭代器对象
while (it.hasNext()){//判断迭代器中是否有下一个元素
//如果有获取元素打印出来
System.out.println(it.next());
}
}
}

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//数组遍历
public class ArrayTraversal {
public static void main(String[] args) {
int[] arr = new int[]{1,2,3};
//fori 取索引
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
//for 取元素
for (int i : arr) {
System.out.println(i);
}
//迭代器
for (int i : arr) {
System.out.println(i);
}
}
}