第30 章 ： Set集合
130 Set接口简介
Set集合不允许保存重复数据
继承关系
-@Iterable -@Collection -@Set -@SortedSet -@NavigableSet AbstractCollection(Collection) -AbstractSet(Set) -HashSet(Set, Cloneable, java.io.Serializable) -TreeSet(NavigableSet, Cloneable, java.io.Serializable)
131 HashSet子类
HashSet元素无序
import java.util.HashSet; import java.util.Set; class Demo{ public static void main(String[] args) { Set<String> list = new HashSet<String>(); list.add("Hello"); list.add("Hello"); list.add("World"); System.out.println(list); // [Hello, World] list.forEach(System.out::println); /** Hello World */ } }
132 TreeSet子类
TreeSet数据有序，按照升序排序
import java.util.Set; import java.util.TreeSet; class Demo{ public static void main(String[] args) { Set<String> list = new TreeSet<String>(); list.add("Hello"); list.add("Hello"); list.add("World"); System.out.println(list); // [Hello, World] list.forEach(System.out::println); /** Hello World */ } }
133 分析TreeSet子类排序操作
TreeSet 通过TreeMap实现
需要实现Comparable接口
自定义类需要将所有属性进行比对，首选HashSet
import java.util.Set; import java.util.TreeSet; class Person implements Comparable<Person> { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } @Override public int compareTo(Person other) { if (this.age > other.age) { return 1; } else if (this.age < other.age) { return -1; } else { return this.name.compareTo(other.name); } } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'; } } class Demo { public static void main(String[] args) { Set<Person> list = new TreeSet<Person>(); list.add(new Person("Jack", 24)); list.add(new Person("Tom", 23)); list.add(new Person("Tom", 23)); System.out.println(list); // [Person{name='Tom', age=23}, Person{name='Jack', age=24}] list.forEach(System.out::println); /** Person{name='Tom', age=23} Person{name='Jack', age=24} */ } }
134 分析重复元素消除
实现重复元素判断
TreeSet Comparable接口
HashSet 对象编码 hashCode方法 ; 对象比较 equals方法
import java.util.HashSet; import java.util.Objects; import java.util.Set; class Person implements Comparable<Person> { private String name; private int age; public Person(String name, int 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; Person person = (Person) o; return age == person.age && Objects.equals(name, person.name); } @Override public int hashCode() { return Objects.hash(name, age); } @Override public int compareTo(Person other) { if (this.age > other.age) { return 1; } else if (this.age < other.age) { return -1; } else { return this.name.compareTo(other.name); } } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'; } } class Demo { public static void main(String[] args) { Set<Person> list = new HashSet<Person>(); list.add(new Person("Jack", 24)); list.add(new Person("Tom", 23)); list.add(new Person("Tom", 23)); System.out.println(list); // [Person{name='Tom', age=23}, Person{name='Jack', age=24}] list.forEach(System.out::println); /** Person{name='Tom', age=23} Person{name='Jack', age=24} */ } }
