List Stream distinct() 去重

List Stream 對象調用distinct()方法，distinct（）不提供按照屬性對對象列表進行去重的直接實現。它是基於hashCode（）和equals（）工作的；
判斷兩個對象是否相同原理與HashMap定位key原理相同，先計算hashCode，如果hashCode相同繼續調用equals()方法。

 

1. Stream.distinct()

distinct()方法的聲明如下：

Stream<T> distinct()

 

2.示例：

package com.concretepage;
public class Book {
private String name;
private int price;
public Book(String name, int price) {
this.name = name;
this.price = price;
}
public String getName() {
return name;
}
public int getPrice() {
return price;
}
@Override
public boolean equals(final Object obj) {
if (obj == null) {
return false;
}
final Book book = (Book) obj;
if (this == book) {
return true;
} else {
return (this.name.equals(book.name) && this.price == book.price);
}
}
@Override
public int hashCode() {
int hashno = 7;
hashno = 13 * hashno + (name == null ? 0 : name.hashCode());
return hashno;
}
}

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 + '}';
    }
}