java8 数据集过滤removeIf和filter

Posted 2022-04-13 tiandi

对象如下，需求：只要30岁以下的人

//求职者的实体类
public class Person 
    private String name;//姓名
    private Integer age;//年龄
    private String gender;//性别

    ...
    //省略构造方法和getter、setter方法
    ...

    //重写toString，方便观看结果
    @Override
    public String toString() 
        return "Person" +
                "name=‘" + name + ‘\‘‘ +
                ", age=" + age +
                ", gender=‘" + gender + ‘\‘‘ +
                ‘‘;
    

1、使用Iterator的传统写法

Collection<Person> collection = new ArrayList();
collection.add(new Person("张三", 22, "男"));
collection.add(new Person("李四", 19, "女"));
collection.add(new Person("王五", 34, "男"));
collection.add(new Person("赵六", 30, "男"));
collection.add(new Person("田七", 25, "女"));
//过滤30岁以上的求职者
Iterator<Person> iterator = collection.iterator();
while (iterator.hasNext()) 
    Person p = iterator.next();
    if (p.getAge() >= 30)
        iterator.remove();

System.out.println(collection.toString());//查看结果

2、不用lambda的removeIf写法

Collection<Person> collection = new ArrayList();
collection.add(new Person("张三", 22, "男"));
collection.add(new Person("李四", 19, "女"));
collection.add(new Person("王五", 34, "男"));
collection.add(new Person("赵六", 30, "男"));
collection.add(new Person("田七", 25, "女"));

collection.removeIf(new Predicate<Person>() 
    @Override
    public boolean test(Person p) 
        return p.getAge()>=30;//过滤30岁以上的求职者
    
);

System.out.println(collection.toString());//查看结果

3、使用lambda的removeIf写法（只有一行了，哈哈）

Collection<Person> collection = new ArrayList();
collection.add(new Person("张三", 22, "男"));
collection.add(new Person("李四", 19, "女"));
collection.add(new Person("王五", 34, "男"));
collection.add(new Person("赵六", 30, "男"));
collection.add(new Person("田七", 25, "女"));


collection.removeIf(p -> p.getAge() >= 30);//过滤30岁以上的求职者

System.out.println(collection.toString());//查看结果

4、使用lambda的filter写法

Collection<Person> collection = new ArrayList();
collection.add(new Person("张三", 22, "男"));
collection.add(new Person("李四", 19, "女"));
collection.add(new Person("王五", 34, "男"));
collection.add(new Person("赵六", 30, "男"));
collection.add(new Person("田七", 25, "女"));

Stream<Person> personStream = collection.stream().filter(p -> p.getAge() < 30)).collect(Collectors.toList());
//由于使用了stream因此后面需要使用.collect(Collectors.toList())转换成list


System.out.println(collection.toString());//查看结果

下面是没有使用lambda的写法

Collection<Person> collection = new ArrayList();
collection.add(new Person("张三", 22, "男"));
collection.add(new Person("李四", 19, "女"));
collection.add(new Person("王五", 34, "男"));
collection.add(new Person("赵六", 30, "男"));
collection.add(new Person("田七", 25, "女"));

Stream<Person> personStream = collection.stream().filter(new Predicate<Person>() 
    @Override
    public boolean test(Person p) 
         return p.getAge() < 30;//只保留男性
    
);

collection = personStream.collect(Collectors.toList());//将Stream转化为List
System.out.println(collection.toString());//查看结果