集合框架--任务：去除重复元素_.keyset().iterator()去除重复-优快云博客

用List去除重复元素

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class LinkedListTest {

    public static void main(String[] args) {

        List list = new ArrayList();

        list.add(new Student("李四", 21));
        list.add(new Student("张三", 20));
        list.add(new Student("王二", 23));
        list.add(new Student("小黄", 24));
        list.add(new Student("李四", 21));

        getSingleElement(list);

    }

    public static void getSingleElement(List list) {

        // 临时容器 存放唯一性元素
        List temp = new ArrayList();

        // 遍历原容器
        for (Iterator it = list.iterator(); it.hasNext();) {
            Object obj = (Object) it.next();

            // 判断是否存在，如果不存在则将所读取的元素传入临时容器中
            if (!temp.contains(obj)) {
                temp.add(obj);
            }
        }

        // 唯一性的元素已经被记录到临时容器中
        // 清空原容器中的元素
        list.clear();

        System.out.println(list);

        // 把临时容器中的元素添加到原容器中
        list.addAll(temp);

        System.out.println(list);

    }
}

package ch;

public class Student {

    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + "]";
    }
    @Override
    public boolean equals(Object obj) {

        System.out.println("判断equlas被调用次数，可说明重复次数");
        if(this == obj){
            return true;
        }
            if(!(obj instanceof Student)){
                return false;
            }

        Student stu = (Student)obj;


        return this.name.equals(stu.name) && this.age == stu.age;
    }
}

用Set接口去除重复元素

*set接口的特点：不包含重复的元素集合

*但是对于自定义对象仍包含有重复对象，则需要用HashSet();
*HashSet：哈希表结构，保证元素唯一性的方式要依赖于hashCode方法和equals方法。

*哈希算法也称为散列算法，所得结果称哈希值
*优：存储的元素是通过哈希值对应关系，该数组为哈希表，查询
速度比数组要快。
*劣：重复元素无法储存，因为要保证元素的唯一性

*当哈希值相同时（hashCode()一致），发生哈希冲突，再次判断元素的内容是否相同（equals()）

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class SetDemo {

    public static void main(String[] args) {

        Set set = new HashSet();

        set.add(new Student("小黄", 24));
        set.add(new Student("李四", 21));
        set.add(new Student("张三", 20));
        set.add(new Student("王二", 23));
        set.add(new Student("小黄", 24));
        set.add(new Student("李四", 21));

        for (Iterator iterator = set.iterator(); iterator.hasNext();) {
            Object object = (Object) iterator.next();
            System.out.println(object);
        }
    }
}

public class Student {

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + "]";
    }

    @Override
    public boolean equals(Object obj) {

        System.out.println("判断equlas被调用次数，可说明重复次数");
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof Student)) {
            return false;
        }

        Student stu = (Student) obj;

        return this.name.equals(stu.name) && this.age == stu.age;
    }

    @Override
    public int hashCode() {

        return name.hashCode() + age;
    }

}