java--set

TreeSet:有序,无重复元素

注意:

有序:要实现Comparable接口, 重复:根据Comparable的返回值为0来判断两个元素是否相同

public class test {    public static void main(String args[]) throws Exception {        Set<Book> all = new TreeSet<>();        all.add(new Book("Java开发",45.6));        all.add(new Book("Java开发",45.6));        all.add(new Book("JSP开发",45.6));        all.add(new Book("Android开发",89.56));        System.out.println(all);    }}class Book implements Comparable<Book>{    private String title;    private double price;    public Book(String title, double price) {        this.title = title;        this.price = price;    }    @Override    public int compareTo(Book o) {        if(this.price > o.price){            return  1;        }else  if(this.price < o.price) {            return  -1;        }else{            return this.title.compareTo(o.title);        }    }    @Override    public String toString() {        return "Book{" +                "title='" + title + '\'' +                ", price=" + price +                '}';    }}

HashSet:无序,不重复

注意:判断不重复的两个步骤

1)取得哈希码:public int hashCode()
  先判断对象的哈希码是否相同,依靠哈希码取得一个对象的内容

2)对象比较:public boolean equals(Object obj)
    再将对象的属性进行一次的比较

public class test {    public static void main(String args[]) throws Exception {        Set<Book> all = new HashSet<>();        all.add(new Book("Java开发",45.6));        all.add(new Book("Java开发",45.6));        all.add(new Book("JSP开发",45.6));        all.add(new Book("Android开发",89.56));        System.out.println(all);    }}class Book {    private String title;    private double price;    public Book(String title, double price) {        this.title = title;        this.price = price;    }    @Override    public boolean equals(Object o) {        if (this == o) return true;        if (o == null || getClass() != o.getClass()) return false;        Book book = (Book) o;        if (Double.compare(book.price, price) != 0) return false;        return title != null ? title.equals(book.title) : book.title == null;    }    @Override    public int hashCode() {        long temp = Double.doubleToLongBits(price);        return (int) (temp ^ (temp >>> 32));    }    @Override    public String toString() {        return "Book{" +                "title='" + title + '\'' +                ", price=" + price +                '}';    }}