为什么 Java 的 map.put 方法返回 old value - V2EX
mangomickey
V2EX    Java

为什么 Java 的 map.put 方法返回 old value

  •  
  •   mangomickey Sep 2, 2019 4478 views
    This topic created in 2445 days ago, the information mentioned may be changed or developed.

    从功能来说,这样返回确实很好用。但是不觉得很别扭吗?

    11 replies    2019-09-29 17:56:08 +08:00
    lanterboy
        1
    lanterboy  
       Sep 2, 2019
    你都说了 从功能来说确实很好用了 那还说啥
    lihongjie0209
        2
    lihongjie0209  
       Sep 2, 2019
    不返回你怎么知道你覆盖了什么值
    chendy
        3
    chendy  
       Sep 2, 2019
    你都说真香了,还有什么好说的…
    wa8n
        4
    wa8n  
       Sep 2, 2019 via iPhone
    香就完了
    HansCathy
        5
    HansCathy  
       Sep 3, 2019
    存在即合理
    LeeSeoung
        6
    LeeSeoung  
       Sep 3, 2019
    那你期望什么值,new value ?你自己 put 的拿不到么,put 之前需要判断是否有 old value,有需要返回,先写 get 再 put ? so,给你返回 old value。
    x66
        7
    x66  
       Sep 3, 2019
    确实想不到都使用 put()来覆盖 oldValue 了,还有什么场景会在后面用到 oldValue
    401825317
        8
    401825317  
       Sep 3, 2019
    @x66
    比如只是想替换一下 key 的名称
    Map<String, Object> param = JSON.parseObject(JSON.toJSONString(userModel, filter));
    param.put("a", param.remove("headurl"));
    param.put("b", param.remove("gender"));
    param.put("c", param.remove("level"));
    param.put("d", param.remove("userprivilegelong"));
    balaWgc
        9
    balaWgc  
       Sep 3, 2019
    赞同 6 楼,你自己 put 的 newValue 还需要返回给你吗,这不是脱裤子放屁吗
    x66
        10
    x66  
       Sep 3, 2019
    @401825317 #8 直接 param.get()不行么
    tffy
        11
    tffy  
       Sep 29, 2019 via iPhone
    不怪,oldValue 被挤出来了
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