ArrayList() 输出

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class zengzhiwei {
public static void main(String agrs[]) {
System.out.println("hello world!");
Map<String, String> m = new HashMap<String, String>();
m.put("zengzhiwei", "zzw");
m.put("zengzhijie", "zzj");

Set<String> s = m.keySet();
Iterator<String> itr = s.iterator();
while(itr.hasNext()) {
Object o = itr.next();
System.out.println(m.get(o));
}

List<Integer> l = new ArrayList<Integer>();
l.add(1);
l.add(2);
l.add(3);
System.out.println(l.toString());
for (int i = 0; i < l.size(); i++) {
System.out.println(l.get(i));

}

}

}

hello world!
zzw
zzj
[1, 2, 3]
1
2
3