Traversal methods for Java collections Set List and Map

The example of this article describes the Java Set, List, Map traversal methods, to share with you for your reference.

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<? extends Object> c){
    Iterator<? extends Object> it = c.iterator();
    while (it.hasNext()) {
      Object object = (Object) it.next();
      System.out.println(object);
    }
  }
  
  @Test
  public void demo1(){
    Set<String> set = new HashSet<String>();
    set.add("AAA");
    set.add("BBB");
    set.add("CCC");
    print(set);
    
    //The first method of traversing a Set: using the Iterator
    Iterator<String> it1 = set.iterator();
    for (String ss : set) {
      System.out.println(ss);
    }
    //The first traversal of a Set: use foreach
    for (String sss : set) {
      System.out.println(sss);
    }
    
    List<String> list = new ArrayList<String>();
    list.add("DDDDD");
    list.add("EEEEE");
    list.add("FFFFF");
    print(list);
    
    //The first way of traversing a List: because the List is in order, get it using the size() and get() methods
    for (int i = 0; i < list.size(); i++) {
      System.out.println(list.get(i));
    }
    //The second way to iterate over a List is with the Iterator
    Iterator<String> it = list.iterator();
    while (it.hasNext()) {
      System.out.println(it.next());
    }
    //The third way of traversing a List: using foreach
    for (String s2 : list) {
      System.out.println(s2);
    }
    
    Map<String,String> map = new TreeMap<String, String>();
    map.put("Jerry", "10000");
    map.put("shellway", "20000");
    map.put("Kizi", "30000");
    print(map.entrySet());
    //The first way to iterate over a Map is to get the key and then the value
    Set<String> sett = map.keySet();
    for (String s : sett) {
      System.out.println(s+":"+map.get(s));
    }
    //The second way of traversing a Map is to get a key-value pair
    for (Map.Entry<String, String> entry : map.entrySet()) {
      System.out.println(entry.getKey()+" : "+entry.getValue());
    }
  }
}

Generics are used here for type safety checking and traversal of collection objects.

I hope this article will be helpful to your Java programming study.