The examples in this article describe the traversal methods of Java collections Set, List, and Map, and share them with you for your reference.
The specific methods are as follows:
package com.shellway.javase; import java.util.ArrayList; import java.util.Collection; import java.util.HashSet; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.Set; import java.util.TreeMap; import org.junit.Test; public class TestCollection { public static void print(Collection c){ Iterator it = c.iterator(); while (it.hasNext()) { Object object = (Object) it.next(); System.out.println(object); } } @Test public void demo1(){ Set set = new HashSet(); set.add("AAA"); set.add("BBB"); set.add("CCC"); print(set); //The first traversal method of Set: using Iterator Iterator it1 = set.iterator(); for (String ss : set) { System.out.println(ss); } //The first traversal method of Set: using foreach for (String sss : set) { System.out.println(sss); } List list = new ArrayList(); list.add("DDDDD"); list.add("EEEEE"); list.add("FFFFF"); print(list); //The first traversal method of List: because the list has order, use the size() and get() methods to obtain for (int i = 0; i <list.size(); i++) { System.out.println(list.get(i)); } //The second way to traverse List: using Iterator Iterator it = list.iterator(); while (it.hasNext()) { System.out.println(it.next()); } //The third way to traverse List: using foreach for (String s2 : list) { System.out.println(s2); } Map map = new TreeMap(); map.put("Jerry", "10000"); map.put("shellway", "20000"); map.put("Kizi", "30000"); print(map.entrySet()); //The first traversal method of Map: first get the key, then get the value Set sett = map.keySet(); for (String s : sett) { System.out.println(s+":"+map.get(s)); } //The second traversal method of Map: obtain key-value pairs for (Map.Entry entry : map.entrySet()) { System.out.println(entry.getKey()+" : "+entry.getValue()); } } }
Generics are used here to perform type safety checking and traversal of collection objects.
I hope this article will be helpful to everyone’s learning of Java programming.