List
是一个接口实现可重复有序的存储,有ArrayList和Linked List两种实现类中使用的方法为add()list.iterrator获得迭代器,通过迭代器进行遍历
区别在于数组和链表的区别
数组查询容易,增加和删除难,
链表增删容易,查询需要遍历;
Set
一个不可重复无序的存储方式,也是常用方法为add和list.iterrator获得迭代器来遍历
hashSet底层为hashmap当我们判断是否为相同值的时候需要同时覆写hashcode和equals方法
TreeSet判断重复为自然排序和定制排序(类似于中介者模式)
自然排序为实现comparable接口实现comparaTO方法的返回值如果为0就不可重复,如果为1或者-1为可重复
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package cn.jiedada.TreeSet; import java.util.Comparator; import java.util.TreeSet; public class Test { /*也是Set的实现类 * 不可重复的无序存储 * 遍历方法 * 不可重复的实现 * 自然排序compareTo和定制排序Comparable这个接口 * 定制排序 * */ public static void main(String[] args) { // TODO Auto-generated method stub TreeSet treeSet = new TreeSet(); Teacher teacher1 = new Teacher("李老师", 42); Teacher teacher2 = new Teacher("李老师", 42); //在添加的时候只能添加同一类的实列 /* Exception in thread "main" java.lang.ClassCastException: cn.jiedada.TreeSet.Teacher cannot be cast to java.lang.Comparable*/ treeSet.add(teacher1); treeSet.add(teacher2); /*Exception in thread "main" java.lang.ClassCastException: * cn.jiedada.TreeSet.Teacher cannot be cast to java.lang.Integer*/ //treeSet.add(1); System.out.println(treeSet); /*TreeSet(Comparator<? super E> comparator) */ } } class Teacher implements Comparable{ String name; Integer age; public Teacher(String name, Integer age) { super(); this.name = name; this.age = age; } @Override public int compareTo(Object o) { // TODO Auto-generated method stub return 0; } @Override public String toString() { return "Teacher [name=" + name + ", age=" + age + "]"; } }
定制排序为compartor接口我们可以为我们自己指定的规则判断是否重复
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
package cn.jiedada.TreeSet; import java.util.Comparator; import java.util.TreeSet; public class Test1 { public static void main(String[] args) { // TODO Auto-generated method stub TreeSet treeSet=new TreeSet(new Comparator() { @Override public int compare(Object o1, Object o2) { Student student1=(Student)o1; Student student2=(Student)o2; return student1.age.compareTo(student2.age); } }); Student student = new Student("李鹏", 18); Student student2 = new Student("小张", 18); treeSet.add(student); treeSet.add(student2); System.out.println(treeSet); } } class Student{ String name; Integer age; public Student(String name, Integer age) { super(); this.name = name; this.age = age; } }