标签:遍历 Java String List list Set new News public
遍历List
首先来创建一个实体类,以供下面使用。
public class News{
private int id;
private String title;
private String author;
public News(int id, String title, String author) {
super();
this.id = id;
this.title = title;
this.author = author;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
}
第一种、最基础的遍历方式:for循环,指定下标长度,使用List集合的size()方法,进行for循环遍历
import java.util.ArrayList;
public class Demo01 {
public static void main(String[] args) {
ArrayList<News> list = new ArrayList<News>();
list.add(new News(1,"list1","a"));
list.add(new News(2,"list2","b"));
list.add(new News(3,"list3","c"));
list.add(new News(4,"list4","d"));
for (int i = 0; i < list.size(); i++) {
News s = (News)list.get(i);
System.out.println(s.getId()+" "+s.getTitle()+" "+s.getAuthor());
}
}
}
第二种、较为简洁的遍历方式:使用foreach遍历List,但不能对某一个元素进行操作(这种方法在遍历数组和Map集合的时候同样适用)
import java.util.ArrayList;
public class Demo02 {
public static void main(String[] args) {
ArrayList<News> list = new ArrayList<News>();
list.add(new News(1,"list1","a"));
list.add(new News(2,"list2","b"));
list.add(new News(3,"list3","c"));
list.add(new News(4,"list4","d"));
for (News s : list) {
System.out.println(s.getId()+" "+s.getTitle()+" "+s.getAuthor());
}
}
}
第三种、适用迭代器Iterator遍历:直接根据List集合的自动遍历
import java.util.ArrayList;
public class Demo03 {
public static void main(String[] args) {
ArrayList<News> list = new ArrayList<News>();
list.add(new News(1,"list1","a"));
list.add(new News(2,"list2","b"));
list.add(new News(3,"list3","c"));
list.add(new News(4,"list4","d"));
Iterator<News> iter = list.iterator();
while (iter.hasNext()) {
News s = (News) iter.next();
System.out.println(s.getId()+" "+s.getTitle()+" "+s.getAuthor());
}
}
}
遍历Map
public static void main(String[] args) {
Map<String, String> map = new HashMap<String, String>();
map.put("1", "value1");
map.put("2", "value2");
map.put("3", "value3");
//第一种:普遍使用,二次取值
System.out.println("通过Map.keySet遍历key和value:");
for (String key : map.keySet()) {
System.out.println("key= "+ key + " and value= " + map.get(key));
}
//第二种
System.out.println("通过Map.entrySet使用iterator遍历key和value:");
Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, String> entry = it.next();
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第三种:推荐,尤其是容量大时
System.out.println("通过Map.entrySet遍历key和value");
for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第四种
System.out.println("通过Map.values()遍历所有的value,但不能遍历key");
for (String v : map.values()) {
System.out.println("value= " + v);
}
}
遍历Set
对 set 的遍历
1.迭代遍历:
Set<String> set = new HashSet<String>();
Iterator<String> it = set.iterator();
while (it.hasNext()) {
String str = it.next();
System.out.println(str);
}
2.for循环遍历:
for (String str : set) {
System.out.println(str);
}
标签:遍历,Java,String,List,list,Set,new,News,public 来源: https://blog.csdn.net/xiaokanfuchen86/article/details/117754053
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