Java: Record

/**
 * 版权所有 2022 涂聚文有限公司
 * 许可信息查看：
 * 描述：
 *
 * 历史版本： JDK 17.01
 * 2022-09-12 创建者 geovindu
 * 2022-09-12 添加 Lambda
 * 2022-09-12 修改：date
 * 接口类
 * 2022-09-12 修改者：Geovin Du
 * 生成API帮助文档的指令：
 *javadoc - -encoding Utf-8 -d apidoc DuRecord.java
 * Interface
 * Record
 * Annotation
 * Enum
 * */



package CoreJava.twelfth;

import java.util.*;

/**
 *
 *
 * */
public class DuRecord {

    /**
     *
     *
     * */
    public record Point(double x, double y)
    {
        // A custom constructor
        public Point() { this(0, 0); }
        // A method
        public double distanceFromOrigin()
        {
            return Math.hypot(x, y);
        }
        // A static field and method
        public static Point ORIGIN = new Point();
        public static double distance(Point p, Point q)
        {
            return Math.hypot(p.x - q.x, p.y - q.y);
        }
    }
    /**
     *
     *
     * */
    public record PointInTime(double x, double y, Date when) { }
    /**
     *
     *
     * */
    public record Range(int from, int to)
    {
        // A compact constructor
        public Range
        {
            if (from > to) // Swap the bounds
            {
                int temp = from;
                from = to;
                to = temp;
            }
        }
    }


}

　　

调用：

// Record
            DuRecord.Point pgeovindu =new DuRecord.Point(3, 4);
            System.out.println("pgeovindu 坐标: " + pgeovindu.x() + " " + pgeovindu.y());
            System.out.println("距离原点: " + pgeovindu.distanceFromOrigin());
            // Same computation with static field and method
            System.out.println("距离原点: " +  DuRecord.Point.distance( DuRecord.Point.ORIGIN, pgeovindu));

            // A mutable record
            var ptgeovindu = new  DuRecord.PointInTime(3, 4, new Date());
            System.out.println("前: " + ptgeovindu);
            ptgeovindu.when().setTime(0);
            System.out.println("后: " + ptgeovindu);

            // Invoking a compact constructor

            var rgeovindu = new  DuRecord.Range(4, 3);
            System.out.println("rgeovindu: " + rgeovindu);

　　

输出：

pgeovindu 坐标: 3.0 4.0
距离原点: 5.0
距离原点: 5.0
前: PointInTime[x=3.0, y=4.0, when=Sun Oct 30 18:45:44 CST 2022]
后: PointInTime[x=3.0, y=4.0, when=Thu Jan 01 08:00:00 CST 1970]
rgeovindu: Range[from=3, to=4]