Java Examples - Collection Traversal
Java ExamplesThe following examples demonstrate how to traverse collections that extend from the Collection interface, namely List, Set, and Map type collections that store data in key-value pairs. Below we use ordinary for, enhanced for, iterator, and other methods to traverse the collections:
Traversal of List and Set Type Collections
Main.java file
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
public class Main {
public static void main(String[] args) {
//Traversal of List Collections
listTest();
//Traversal of Set Collections
setTest();
}
private static void setTest() {
Set<String> set = new HashSet<String>();
set.add("JAVA");
set.add("C");
set.add("C++");
//Duplicate data addition failed
set.add("JAVA");
set.add("JAVASCRIPT");
//Using iterator to traverse set collections
Iterator<String> it = set.iterator();
while (it.hasNext()) {
String value = it.next();
System.out.println(value);
}
//Using enhanced for loop to traverse set collections
for(String s: set){
System.out.println(s);
}
}
//Traversing list collections
private static void listTest() {
List<String> list = new ArrayList<String>();
list.add("Vegetable");
list.add("Bird");
list.add("Teach");
list.add("Course");
list.add("www.example.com");
//Using iterator to traverse
Iterator<String> it = list.iterator();
while (it.hasNext()) {
String value = it.next();
System.out.println(value);
}
//Using traditional for loop to traverse
for (int i = 0, size = list.size(); i < size; i++) {
String value = list.get(i);
System.out.println(value);
}
//Using enhanced for loop to traverse
for (String value : list) {
System.out.println(value);
}
}
}
The output of the above code is:
菜 鸟 教 程 www.example.com 菜 鸟 教 程 www.example.com 菜 鸟 教 程 www.example.com JAVA JAVASCRIPT C++ C JAVA JAVASCRIPT C++ C
About Traversal of Map Type Collections
In the following example, we use HashMap's keySet() and entrySet() methods to traverse the collection:
/*
author by example.com
Main.java
*/
import java.util.Map;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.Map.Entry;
//增强For循环
public class Main {
public static void main(String[] args) {
// 创建一个HashMap对象,并加入了一些键值对。
Map<String, String> maps = new HashMap<String, String>();
maps.put("1", "PHP");
maps.put("2", "Java");
maps.put("3", "C");
maps.put("4", "C++");
maps.put("5", "HTML");
// 传统的遍历map集合的方法1; keySet()
//traditionalMethod1(maps);
// 传统的遍历map集合的方法2; entrySet()
//traditionalMethod2(maps);
// 使用增强For循环来遍历map集合方法1; keySet()
//strongForMethod1(maps);
// 使用增强For循环来遍历map集合方法2; entrySet()
strongForMethod2(maps);
}
private static void strongForMethod2(Map<String, String> maps) {
Set<Entry<String, String>> set = maps.entrySet();
for (Entry<String, String> entry : set) {
String key = entry.getKey();
String value = entry.getValue();
System.out.println(key + " : " + value);
}
}
private static void strongForMethod1(Map<String, String> maps) {
Set<String> set = maps.keySet();
for (String s : set) {
String key = s;
String value = maps.get(s);
System.out.println(key + " : " + value);
}
}
// 使用entrySet()方法，获取maps集合中的每一个键值对，
private static void traditionalMethod2(Map<String, String> maps) {
Set<Map.Entry<String, String>> sets = maps.entrySet();
// 取得迭代器遍历出对应的值。
Iterator<Entry<String, String>> it = sets.iterator();
while (it.hasNext()) {
Map.Entry<String, String> entry = (Entry<String, String>) it.next();
String key = entry.getKey();
String value = entry.getValue();
System.out.println(key + " : " + value);
}
}
// 使用keySet()方法，获取maps集合中的所有键，遍历键取得所对应的值。
private static void traditionalMethod1(Map<String, String> maps) {
Set<String> sets = maps.keySet();
// 取得迭代器遍历出对应的值
Iterator<String> it = sets.iterator();
while (it.hasNext()) {
String key = it.next();
String value = maps.get(key);
System.out.println(key + " : " + value);
}
}
}
The output of the above code is:
1 : PHP 2 : Java 3 : C 4 : C++ 5 : HTMLOther Extensions