List循环与Map循环的总结

@Test
public void ForListTest() {
List<String> list = new ArrayList<String>();
list.add("1");
list.add("2");
list.add("3");
list.add("4");
list.add("5");

// 迭代器循环不需要知道集合的大小以及类型，最佳选择
for (@SuppressWarnings("rawtypes")
Iterator iterator = list.iterator(); iterator.hasNext();) {
String list = (String) iterator.next();
System.out.println("01)Iterator for：===============" + list);
}

// foreach相对比for来讲，不需要知道集合的长度
for (String list : list) {
System.out.println("02)foreach:=================" + list);
}

// for循环既需要知道集合的大小，而且要求是有序的
for (int i = 0; i < list.size(); i++) {
System.out.println("03)for==================" + list.get(i));
}
}

@Test
public void ForMapTest() {
Map<String, String> map = new HashMap<String, String>();
map.put("01", "1");
map.put("02", "2");
map.put("03", "3");
map.put("04", "4");
map.put("05", "5");
Set<String> keySet = map.keySet();
//1.keyset的foreach方法
for (String key : keySet) {
System.out.println("1)keyset:" + "key:" + key + " value:"
+ map.get(key));
}

Set<Entry<String, String>> entrySet = map.entrySet();
//2.entryset的迭代方法
for (@SuppressWarnings("rawtypes")
Iterator iterator = entrySet.iterator(); iterator.hasNext();) {
@SuppressWarnings("unchecked")
Entry<String, String> entry = (Entry<String, String>) iterator
.next();
System.out.println("02)entrySet,iterator: key:" + entry.getKey()
+ " value:" + entry.getValue());
}

//3.推荐，容量最大
for (Entry<String, String> entry : entrySet) {
System.out.println("03)entrySet,foreach:key:" + entry.getKey()
+ " value:" + entry.getValue());
}

Collection<String> values = map.values();
//4.只循环出value的方法
for (String value : values) {
System.out.println("04)values,just for values,value:" + value);
}

}