使用静态方法代替构造器创建实例

简介

在一些业务场景下，我们为了程序灵活性，需要通过构造多个参数的构造器来创建实例。由于参数的多样性，会给创建者带来一定的困惑，这种情况下可以考虑使用静态方法来创建实例。

示例

public class Result<T> {
    //业务结果标识
    private boolean flag;
    //http 状态码
    private int code;
    //业务结果消息
    private String msg;
    //业务数据
    private T data;

    public Result(){
        this.flag = true;
        this.code = 200;
        this.msg = "success";
    }

    public Result(boolean flag, String msg){
        this.flag = flag;
        this.msg = msg;
        this.code = 200;
    }

    public Result(boolean flag, int code, String msg){
        this.flag = flag;
        this.code = code;
        this.msg = msg;
    }

    public Result(boolean flag, int code, String msg, T data){
        this.flag = flag;
        this.code = code;
        this.msg = msg;
        this.data = data;
    }

    public boolean isFlag() {
        return flag;
    }

    public void setFlag(boolean flag) {
        this.flag = flag;
    }

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

    @Override
    public String toString() {
        return "Result{" +
                "flag=" + flag +
                ", code=" + code +
                ", msg='" + msg + '\'' +
                ", data=" + data +
                '}';
    }
}

调用

@Test
public void tt(){
    //业务处理成功，并返回业务数据
    Result result = new Result(true, 200, "success", "ZhangSan");
    System.out.println(result);
    //处理成功，无业务数据
    result = new Result();
    System.out.println(result);
    //处理失败，无业务数据
    result = new Result(false, "handle faild");
    System.out.println(result);
    //系统级http错误码
    result = new Result(false, 400, "Bad Request");
    System.out.println(result);
}

使用静态方法创建实例

public class Result<T> {
    //业务结果标识
    private boolean flag;
    //http 状态码
    private int code;
    //业务结果消息
    private String msg;
    //业务数据
    private T data;

    private Result(){
        this.flag = true;
        this.code = 200;
        this.msg = "success";
    }

    private Result(boolean flag, String msg){
        this.flag = flag;
        this.msg = msg;
        this.code = 200;
    }

    private Result(boolean flag, int code, String msg){
        this.flag = flag;
        this.code = code;
        this.msg = msg;
    }

    private Result(boolean flag, int code, String msg, T data){
        this.flag = flag;
        this.code = code;
        this.msg = msg;
        this.data = data;
    }

    public static <T> Result okAndData(T data){
        return new Result(true, 200, "success", data);
    }

    public static Result ok(){
        return new Result();
    }

    public static Result faild(){
        return new Result(false, 200, "faild", null);
    }

    public static Result faildAndMsg(String msg){
        return new Result(false, 200, msg, null);
    }


    public boolean isFlag() {
        return flag;
    }

    public void setFlag(boolean flag) {
        this.flag = flag;
    }

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

    @Override
    public String toString() {
        return "Result{" +
                "flag=" + flag +
                ", code=" + code +
                ", msg='" + msg + '\'' +
                ", data=" + data +
                '}';
    }
}

调用

@Test
public void tt2(){
    Result result = Result.ok();
    System.out.println(result);
    result = Result.okAndData("ZhangSan");
    System.out.println(result);
    result = Result.faild();
    System.out.println(result);
    result = Result.faildAndMsg("server handle faild");
    System.out.println(result);
}

使用静态方法创建实例好处

• 让创建实例者很清楚的知道要创建的是一个什么功能的实例。
• 可以不必每次都new一个新的实例，你可以自由控制实例个数，比如上面的demo中，针对Result.ok()，可以每次只创建一次。或者如jdk源码中的Integer.valueOf方法，会提前缓存好-128到127的Integer对象，在这个数字范围内的实例，其实是复用的。
• 可以创建一个当前class的子类型实例，类似简单工厂模式，你可以根据不同的参数来返回不同的子类对象。