jdk8 List集合 Stream distinct() 去重代码示例

深藏阁楼爱情的钟 2023-10-07 08:10 25阅读 0赞

> Requirements:  
> 去重List内重复对象（此处重复定义与对象属性值有关）
> 
> Achievement:  
> List Stream 对象调用distinct()方法，distinct()方法依赖hashCode()和equals()方法。  
> 判断两个对象是否相同原理与HashMap定位key原理相同，先计算hashCode，如果hashCode相同继续调用equals()方法。

List<Animal> animals = new ArrayList<>(
            Arrays.asList(
                    new Animal("wangwang", 3),
                    new Animal("wangwang", 3),
                    new Animal("guagua", 2)
            )
    );
    System.out.println(animals);
    System.out.println(animals.stream().distinct().collect(Collectors.toList()));

**Console:**

[Animal{name=‘wangwang’, age=3}, Animal{name=‘wangwang’, age=3}, Animal{name=‘guagua’, age=2}]
    [Animal{name=‘wangwang’, age=3}, Animal{name=‘guagua’, age=2}]

**Animal Class：**

public class Animal {
    
        private String name;
    
        private Integer age;
    
        public Animal(String name, Integer age) {
            this.name = name;
            this.age = age;
        }
    
        @Override
        public boolean equals(Object o) {
            if (this == o)
                return true;
            if (o == null || getClass() != o.getClass())
                return false;
            Animal animal = (Animal) o;
            return Objects.equals(name, animal.name) && Objects.equals(age, animal.age);
        }
    
        @Override
        public int hashCode() {
            return Objects.hash(name, age);
        }
    
        @Override
        public String toString() {
            return "Animal{" + "name='" + name + '\'' + ", age=" + age + '}';
        }
    }