java8遍历集合_【记录】【java】JDK8新特性Stream方式遍历集合
由于是以流方式，所以怎么操作也不改变原来的集合
1、普通遍历forEach
List list = newArrayList();
list.add("a");
list.add("b");
list.add("c");
list.add("d");
List list2 = newArrayList();
list.stream().forEach(str->{
list2.add(str);
});
System.out.println(list2);
2、过滤filter
List list = newArrayList();
list.add("a");
list.add("b");
list.add("c");
list.add("d");
List list3 = newArrayList();//过滤字符串为a的元素
list.stream().filter(str -> !"a".equals(str)).forEach(str ->{
list3.add(str);
});
System.out.println(list3);
3、排序sorted
List list = newArrayList();
list.add("ab");
list.add("aa");
list.add("c");
list.add("d");
System.out.println("操作前list: " +list);
List collect = list.stream().sorted((a, b) ->{returna.compareTo(b);
}).collect(Collectors.toList());
System.out.println("升序collect: " +collect);
List collect2 = list.stream().sorted((a, b) ->{returnb.compareTo(a);
}).collect(Collectors.toList());
System.out.println("降序collect2: " +collect2);
}
4、操作字符串集合，返回拼接字符串。collect的Collectors.joining
List list = newArrayList();
list.add("b");
list.add("a");
list.add("c");
list.add("d");
System.out.println("操作前list: " +list);
String collect= list.stream().sorted((a, b) ->{returnb.compareTo(a);
}).collect(Collectors.joining(",", "前", "后"));
System.out.println("有前后collect: " +collect);
String collect2= list.stream().sorted((a, b) ->{returnb.compareTo(a);
}).collect(Collectors.joining(","));
System.out.println("没前后collect: " + collect2);
5、操作map集合
List> list = newArrayList();
Map map = new HashMap<>();
map.put("id", "wwww");
list.add(map);
Map map2 = new HashMap<>();
map2.put("id", "qqqq");
list.add(map2);
Map map3 = new HashMap<>();
map3.put("name", "qqqq");
list.add(map3);
System.out.println("list: " +list);
String collect= list.stream().filter(map1 -> null != map1.get("id"))
.map(str-> str.get("id").toString())
.collect(Collectors.joining(",", "前", "后"));
System.out.println("collect: " + collect);
6、操作对象
List list = newArrayList();
Student student= newStudent();
student.setAge("11");
student.setName("aaa");
list.add(student);
Student student2= newStudent();
student2.setAge("22");
student2.setName("bbb");
list.add(student2);
System.out.println("list: " +list);
String collect= list.stream().map(student3 ->student3.getName())
.collect(Collectors.joining(",", "前", "后"));
System.out.println("collect: " + collect);
7、合并两个字符串数组flatMap
List list = newArrayList();
list.add(new String[]{"aa", "bb"});
list.add(new String[]{"ff", "ee"});
System.out.println("list: " +list);
String collect=list.stream().flatMap(Arrays::stream)
.collect(Collectors.joining(",", "前", "后"));
System.out.println("collect: " + collect);
8、合并两个字符串集合flatMap
List> list = newArrayList();
list.add(Arrays.asList(new String[]{"aa", "bb"}));
list.add(Arrays.asList(new String[]{"ff", "ee"}));
System.out.println("list: " +list);
String collect= list.stream().flatMap(list2 ->list2.stream())
.collect(Collectors.joining(",", "前", "后"));
System.out.println("collect: " + collect);
9、合并对象集合
List> list = newArrayList();
List list1 = newArrayList();
list1.add(new Student("23", "aaa"));
list1.add(new Student("43", "bbb"));
list.add(list1);
List list2 = newArrayList();
list2.add(new Student("66", "qqq"));
list2.add(new Student("77", "www"));
list.add(list2);
System.out.println("list: " +list);
String collect= list.stream().flatMap(list4 -> list4.stream().map(student ->student.getName()))
.collect(Collectors.joining(",", "前", "后"));
System.out.println("collect: " + collect);
