数组和容器的打印（学习java编程思想笔记）

对于数组的打印，必须使用Arrays.toString()方法来产生数组的的可表示打印，但是打印容器无需任何帮助。

import java.util.Collection;
import java.util.*;

public class PrintingContainers {

static Collection fill(Collection<String> collection) {
collection.add("rat");
collection.add("cat");
collection.add("dog");
collection.add("dog");
return collection;
}
static Map fill(Map<String,String> map) {
map.put("rat", "Fuzzy");
map.put("cat", "Rags");
//一个键只能对应一个值
map.put("dog", "Bosco");
map.put("dog", "Spot");
return map;
}   

public static void main(String[] args) {
  
  System.out.println(fill(new ArrayList<String>()));
  System.out.println(fill(new LinkedList<String>()));
  
  //Set集合中不能保存相同元素
  System.out.println(fill(new HashSet<String>()));
  System.out.println(fill(new TreeSet<String>()));
  System.out.println(fill(new LinkedHashSet<String>()));
  
  System.out.println(fill(new HashMap<String,String>()));
  System.out.println(fill(new TreeMap<String,String>()));
  System.out.println(fill(new LinkedHashMap<String,String>()));
  
  int [] arg = {1,2,3,4};
  System.out.println(Arrays.toString(arg));
}
} /* Output:
[rat, cat, dog, dog]
[rat, cat, dog, dog]
[dog, cat, rat]
[cat, dog, rat]
[rat, cat, dog]
{dog=Spot, cat=Rags, rat=Fuzzy}
{cat=Rags, dog=Spot, rat=Fuzzy}
{rat=Fuzzy, cat=Rags, dog=Spot}
[1, 2, 3, 4]
*/