内部类、HashSet

最新推荐文章于 2024-11-09 14:56:57 发布

原创最新推荐文章于 2024-11-09 14:56:57 发布 · 106 阅读

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此代码示例展示了如何在 Java 中使用 HashSet，并重写 Employee 类及其内部类 MyDate 的 equals 和 hashCode 方法，确保当对象属性相同时，HashSet 能正确处理重复项。程序输出了 HashSet 的大小和内容，演示了 equals 和 hashCode 方法在集合操作中的作用。

package enumeration;

import java.util.HashSet;
import java.util.Objects;

public class HashSet_ {
    public static void main(String[] args) {
        HashSet hashSet = new HashSet();

        Employee milan = new Employee("milan", 12500, new Employee.MyDate(2021, 11, 20));
        Employee jack = new Employee("jack", 12500, new Employee.MyDate(2021, 11, 20));
        Employee tom = new Employee("milan", 12500, new Employee.MyDate(2021, 11, 20));
        hashSet.add(milan);
        hashSet.add(jack);
        hashSet.add(tom);
        System.out.println("hashSet.size = " +hashSet.size());
        System.out.println("hashSet = " + hashSet );
        //重写他们的hashCode,如果name 和Age一样就放回相同的hashCode
//        System.out.println(hashSet);
    }
}

class Employee{
    private String name;
    private double sal;
    private MyDate myDate;

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + '\'' +
                ", sal=" + sal +
                ", myDate=" + myDate +
                '}';
    }

    public Employee(String name, double sal, MyDate myDate) {
        this.name = name;
        this.sal = sal;
        this.myDate = myDate;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return Double.compare(employee.sal, sal) == 0 &&
                Objects.equals(name, employee.name) &&
                Objects.equals(myDate, employee.myDate);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, sal, myDate);
    }

    static class MyDate{
        int year;
        int month;
        int day;

        public MyDate(int year, int month, int day) {
            this.year = year;
            this.month = month;
            this.day = day;
        }

        @Override
        public String toString() {
            return "MyDate{" +
                    "year=" + year +
                    ", month=" + month +
                    ", day=" + day +
                    '}';
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            MyDate myDate = (MyDate) o;
            return year == myDate.year &&
                    month == myDate.month &&
                    day == myDate.day;
        }

        @Override
        public int hashCode() {
            return Objects.hash(year, month, day);
        }
    }
    }