Java知识点-Stream流

Stream流的中间方法

• 中间方法，返回新的Stream流，原来的Stream流只能使用一次，建议使用链式编程
• 修改Stream流中的数据，不会影响原来的集合或者数组中的数据

Stream流的终结方法

• parseInt转换数据类型
• 收集到Map集合，数据不能重复，不然会报错

练习

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;public class Test1 {public static void main(String[] args) {/*定义一个集合,并添加一些整数过滤奇数,只留下偶数。并将结果保存起来 1,2,3,4,5,6,7,8,9,10*///1.定义一个集合ArrayList<Integer> list = new ArrayList<Integer>();//2.添加一些整数Collections.addAll(list, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10);//3.过滤奇数，如果是偶数则保留List<Integer> newList = list.stream().filter(n -> n % 2 == 0).collect(Collectors.toList());System.out.println(newList);}
}

import java.util.ArrayList;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;public class Test2 {public static void main(String[] args) {/*练习:创建一个ArrayList集合,并添加以下字符串,字符串中前面是姓名,后面是年龄"zhangsan,23""lisi,24""wangwu,25"保留年龄大于等于24岁的人,并将结果收集到Map集合中,姓名为键,年龄为值*///1.创建一个ArrayList集合ArrayList<String> list = new ArrayList<>();//2.添加字符list.add("zhangsan,23");list.add("lisi,24");list.add("wangwu,25");//3.保留年龄大于等于24岁的人/*list.stream().filter(s->Integer.parseInt(s.split(",")[1])>=24).collect(Collectors.toMap(new Function<String, String>() {@Overridepublic String apply(String s) {return s.split(",")[0];}}, new Function<String, Integer>() {@Overridepublic Integer apply(String s) {return Integer.parseInt(s.split(",")[1]);}}));*/Map<String, Integer> map = list.stream().filter(s -> Integer.parseInt(s.split(",")[1]) >= 24).collect(Collectors.toMap(s -> s.split(",")[0],s -> Integer.parseInt(s.split(",")[1])));System.out.println(map);}
}

• 可以先写匿名内部类，再写toMap

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;public class Test3 {public static void main(String[] args) {/*现在有两个ArrayList集合,分别存储6名男演员的名字和年车龄以及6名女演员的名字和年龄姓名和年龄中间用逗号隔开。比如:张三,23要求完成如下的操作:1,男演员只要名字为3个字的前两人2,女演员只要姓杨的,并且不要第一个3,把过滤后的男演员姓名和女演员姓名合并到一起4,将上一步的演员姓名封装成Actor对象。5,将所有的演员对象都保存到List集合中。备注:演员类Actor,属性有:name,age男演员:"蔡坤坤,24","叶胸咸,23","刘不甜,22","吴签,24","谷嘉,30","肖梁梁,27女演员:"赵小颖,35","杨颖,36","高元元,43","张天天,31","刘诗,35","杨小幂,33"*///1.创建两个集合ArrayList<String> manList = new ArrayList<String>();ArrayList<String> womenList = new ArrayList<>();//2.添加数据Collections.addAll(manList, "蔡坤坤,24", "叶胸咸,23", "刘不甜,22", "吴签,24", "谷嘉,30", "肖梁梁,27");Collections.addAll(womenList, "赵小颖,35", "杨颖,36", "高元元,43", "张天天,31", "刘诗,35", "杨小幂,33");//3.男演员只要名字为3个字的前两人Stream<String> stream1 = manList.stream().filter(s -> s.split(",")[0].length() == 3).limit(2);//4.女演员只要姓杨的,并且不要第一个Stream<String> stream2 = womenList.stream().filter(s -> s.split(",")[0].startsWith("杨")).skip(1);//5.将上一步的演员姓名封装成Actor对象。/*Stream.concat(stream1,stream2).map(new Function<String,Actor>() {@Overridepublic Actor apply(String s) {String naem = s.split(",")[0];int age = Integer.parseInt(s.split(",")[1]);return new Actor(naem, age);}}).forEach(s->System.out.println(s));*/List<Actor> list = Stream.concat(stream1, stream2).map(s -> new Actor(s.split(",")[0], Integer.parseInt(s.split(",")[1]))).collect(Collectors.toList());//将所有元素收集到List当中System.out.println(list);}
}