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一样平常开发stream流示例

  基础对象代码块

1. @Data
2. @ToString
3. public class Person {
4.     private String name;
5.     private String city;
7.     public Person(String name, String city) {
8.         this.name = name;
9.         this.city = city;
10.     }
11. }

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集合转换示例

  转换为key,object场景

  示例代码

1. List<Person> list = new ArrayList<>();
2.         list.add(new Person("a","aaaaaaaaaaa111"));
3.         list.add(new Person("a","aaaaaaaaaaa222"));
4.         list.add(new Person("a","aaaaaaaaaaa333"));
5.         list.add(new Person("b","bbbbbbbbbbb111"));
6.         list.add(new Person("b","bbbbbbbbbbb222"));
7.         list.add(new Person("b","bbbbbbbbbbb333"));
8.         list.add(new Person("c","ccccccccccc111"));
9.         list.add(new Person("c","ccccccccccc222"));
10.         list.add(new Person("c","ccccccccccc333"));
11.         Map<String, Person> map = list.stream().collect(Collectors.toMap(Person::getName, Function.identity(), (key1, key2) -> key2));
12.         System.out.println(map);
13.         Map<String, Person> map1 = list.stream().collect(Collectors.toMap(Person::getName, Function.identity(), (key1, key2) -> key1));
14.         System.out.println(map1);

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运行效果

1. {a=Person(name=a, city=aaaaaaaaaaa333), b=Person(name=b, city=bbbbbbbbbbb333), c=Person(name=c, city=ccccccccccc333)}
2. {a=Person(name=a, city=aaaaaaaaaaa111), b=Person(name=b, city=bbbbbbbbbbb111), c=Person(name=c, city=ccccccccccc111)}

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转换为key,List<>场景

  示例代码

1. List<Person> list = new ArrayList<>();
2.         list.add(new Person("a","aaaaaaaaaaa111"));
3.         list.add(new Person("a","aaaaaaaaaaa222"));
4.         list.add(new Person("a","aaaaaaaaaaa333"));
5.         list.add(new Person("b","bbbbbbbbbbb111"));
6.         list.add(new Person("b","bbbbbbbbbbb222"));
7.         list.add(new Person("b","bbbbbbbbbbb333"));
8.         list.add(new Person("c","ccccccccccc111"));
9.         list.add(new Person("c","ccccccccccc222"));
10.         list.add(new Person("c","ccccccccccc333"));
11.         Map<String, List<Person>> collect = list.stream().collect(Collectors.groupingBy(item -> item.getName()));
12.         System.out.println(collect);

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运行效果

1. {a=[Person(name=a, city=aaaaaaaaaaa111), Person(name=a, city=aaaaaaaaaaa222), Person(name=a, city=aaaaaaaaaaa333)], b=[Person(name=b, city=bbbbbbbbbbb111), Person(name=b, city=bbbbbbbbbbb222), Person(name=b, city=bbbbbbbbbbb333)], c=[Person(name=c, city=ccccccccccc111), Person(name=c, city=ccccccccccc222), Person(name=c, city=ccccccccccc333)]}

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返回集合中某个字段的set集合

  示例代码

1. private static void getColoumSet() {
2.         List<Person> list = new ArrayList<>();
3.         list.add(new Person("a","aaaaaaaaaaa111"));
4.         list.add(new Person("a","aaaaaaaaaaa222"));
5.         list.add(new Person("a","aaaaaaaaaaa333"));
6.         list.add(new Person("b","bbbbbbbbbbb111"));
7.         list.add(new Person("b","bbbbbbbbbbb222"));
8.         list.add(new Person("b","bbbbbbbbbbb333"));
9.         list.add(new Person("c","ccccccccccc111"));
10.         list.add(new Person("c","ccccccccccc222"));
11.         list.add(new Person("c","ccccccccccc333"));
12.         Set<String> collect = list.stream().map(Person::getName).collect(Collectors.toSet());
13.         System.out.println(collect);
14.         String[] longs = collect.toArray(new String[0]);
15.         System.out.println(Arrays.toString(longs));
16.     }

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运行效果

1. [a, b, c]
2. [a, b, c]

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数组转换成集合

  示例代码

1. private static void arraysToSet() {
2.         String[] pigArray = {"猪头", "猪脑", "猪身", "猪尾巴"};
3.         Set<String> pigSet = Arrays.stream(pigArray) .collect(Collectors.toSet());
4.     }

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