Traversal methods for Java collections Set List and Map
- 2020-04-01 03:27:48
- OfStack
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.