JAVA8新特性--集合遍历之forEach

java中的集合有两种形式Collection<E>,Map<K,V>
Collection类型集合

在JAVA7中遍历有以下几种方式:
List<String> list = Arrays.asList("aaaa","bbbb");
------------------------------------------------------------------------------
//for循环
for (int i=0;i< list.size();i++){
System.out.println(list.get(i));
}
------------------------------------------------------------------------------
//增强for循环
for(String str : list){
System.out.println(str);
}
------------------------------------------------------------------------------
//迭代器
Iterator<String> iterator = list.iterator();
while (iterator.hasNext()){
System.out.println(iterator.next());
}

在JAVA8中还可以使用forEach来遍历:
list.forEach(new Consumer<String>() {
@Override
public void accept(String s) {
System.out.println(s);
}
});

发现和使用sort排序的写法是一样的:
Collections.sort(list, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o1.compareTo(o2);
}
});

加上Lambda表达式后,如下:
list.forEach(str-> System.out.println(str));

sort排序也使用Lambda表达式,如下:
Collections.sort(list,(o1,o2)->{return o1.compareTo(o2);});

Map类型集合
在JAVA7中遍历有下面几种方式:
Map<String,String> map = new HashMap<>();
map.put("id","11");
map.put("name","zhangsan");
map.put("age","30");
------------------------------------------------------------------------------
for (Map.Entry<String,String> entry : map.entrySet()){
System.out.println("k=" + entry.getKey() + ",v=" + entry.getValue());
}
------------------------------------------------------------------------------
for (String key : map.keySet()){
System.out.println("k=" + key + ",v=" + map.get(key));
}
------------------------------------------------------------------------------
Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
while (iterator.hasNext()){
Map.Entry<String, String> entry = iterator.next();
System.out.println("k=" + entry.getKey() + ",v=" + entry.getValue());
}
------------------------------------------------------------------------------
for (String v : map.values()){
System.out.println("v=" + v);
}
------------------------------------------------------------------------------
使用JAVA8的forEach遍历,如下:
map.forEach(new BiConsumer<String, String>() {
@Override
public void accept(String s, String s2) {
System.out.println("k=" + s + ",v=" + s2);
}
});

也可以使用Lambda表达式,如下:
map.forEach((k,v)-> System.out.println("v="+k+",v="+v));

 

posted on 2021-07-28 11:46  ALWAYS☆REMIND  阅读(156)  评论(0编辑  收藏  举报

导航