{"id":329,"date":"2023-03-08T08:36:19","date_gmt":"2023-03-08T08:36:19","guid":{"rendered":"https:\/\/www.webagam.com\/pages\/?p=329"},"modified":"2023-03-09T06:05:40","modified_gmt":"2023-03-09T06:05:40","slug":"java-record-record-is-a-class-at-act","status":"publish","type":"post","link":"https:\/\/webagam.com\/pages\/2023\/03\/08\/java-record-record-is-a-class-at-act\/","title":{"rendered":"Java Record, “record is a class (at) act”"},"content":{"rendered":"
1<\/div> \r\n\t\t\t\t\t\t\t\t\t
\r\n\t\t\t\t\t\t\t\t\tClap\r\n\t\t\t\t\t\t\t\t\t<\/span>\r\n\t\t\t\t\t\t\t\t\t<\/div><\/div><\/div>\n

What is a Record?<\/h2>\n\n\n\n

Records in java is a final immutable class that gets the following methods by default,<\/p>\n\n\n\n

    \n
  • constructor<\/li>\n\n\n\n
  • getters or rather member variable accessors to be specific<\/li>\n\n\n\n
  • equals, hashcode and toString<\/li>\n<\/ul>\n\n\n\n

    For example, if we need to write a class to maintain High and Low like below,<\/p>\n\n\n\n

    <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
    package<\/span> <\/span>com<\/span>.<\/span>example<\/span>.<\/span>demo<\/span>;<\/span><\/span>\n<\/span>\npublic<\/span> <\/span>final<\/span> <\/span>class<\/span> <\/span>HiLo<\/span> <\/span>{<\/span><\/span>\n\t<\/span>private<\/span> <\/span>final<\/span> <\/span>int<\/span> <\/span>hi<\/span>;<\/span><\/span>\n\t<\/span>private<\/span> <\/span>final<\/span> <\/span>int<\/span> <\/span>lo<\/span>;<\/span><\/span>\n\t<\/span><\/span>\n\t<\/span>public<\/span> <\/span>HiLo<\/span>(<\/span>int<\/span> <\/span>hi<\/span>,<\/span> <\/span>int<\/span> <\/span>lo<\/span>)<\/span> <\/span>{<\/span><\/span>\n\t\t<\/span>this<\/span>.<\/span>hi<\/span> <\/span>=<\/span> hi<\/span>;<\/span><\/span>\n\t\t<\/span>this<\/span>.<\/span>lo<\/span> <\/span>=<\/span> lo<\/span>;<\/span><\/span>\n\t<\/span>}<\/span><\/span>\n\t<\/span><\/span>\n\t<\/span>public<\/span> <\/span>int<\/span> <\/span>getHi<\/span>()<\/span> <\/span>{<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>this<\/span>.<\/span>hi<\/span>;<\/span><\/span>\n\t<\/span>}<\/span><\/span>\n\t<\/span><\/span>\n\t<\/span>public<\/span> <\/span>int<\/span> <\/span>getLo<\/span>()<\/span> <\/span>{<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>this<\/span>.<\/span>lo<\/span>;<\/span><\/span>\n\t<\/span>}<\/span><\/span>\n\t<\/span><\/span>\n\t<\/span>@<\/span>Override<\/span><\/span>\n\t<\/span>public<\/span> <\/span>int<\/span> <\/span>hashCode<\/span>()<\/span> <\/span>{<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>this<\/span>.<\/span>hi<\/span> <\/span>+<\/span> <\/span>this<\/span>.<\/span>lo<\/span>;<\/span><\/span>\n\t<\/span>}<\/span><\/span>\n\t<\/span><\/span>\n<\/span>\n\t<\/span>public<\/span> <\/span>boolean<\/span> <\/span>equals<\/span>(<\/span>HiLo<\/span> <\/span>hilo<\/span>)<\/span> <\/span>{<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>hilo<\/span>.<\/span>hi<\/span> <\/span>==<\/span> <\/span>this<\/span>.<\/span>hi<\/span> <\/span>&&<\/span> <\/span>hilo<\/span>.<\/span>lo<\/span> <\/span>==<\/span> <\/span>this<\/span>.<\/span>lo<\/span>;<\/span><\/span>\n\t<\/span>}<\/span><\/span>\n\t<\/span><\/span>\n\t<\/span>@<\/span>Override<\/span><\/span>\n\t<\/span>public<\/span> <\/span>String<\/span> <\/span>toString<\/span>()<\/span> <\/span>{<\/span><\/span>\n\t\t<\/span>return<\/span> <\/span>"<\/span>High:<\/span>"<\/span>+<\/span> <\/span>this<\/span>.<\/span>hi<\/span> <\/span>+<\/span> <\/span>"<\/span> low:<\/span>"<\/span> <\/span>+<\/span> <\/span>this<\/span>.<\/span>lo<\/span>;<\/span><\/span>\n\t<\/span>}<\/span><\/span>\n<\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    Until java 16 (The final release of java record) we need to write code like the above, not anymore all of the above can be written in a single line, <\/p>\n\n\n\n
    <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
    package<\/span> <\/span>com<\/span>.<\/span>example<\/span>.<\/span>demo<\/span>;<\/span><\/span>\n<\/span>\npublic<\/span> record HighLow (int high, int low) <\/span>{<\/span> <\/span>}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    Record HighLow is internally a final class that has the following,<\/p>\n\n\n\n
      \n
    • high and low are private final member variables of the class HighLow<\/li>\n\n\n\n
    • constructor which takes high and low as arguments and assigns them to the corresponding member variable<\/li>\n\n\n\n
    • accessor for high and low thru high() and low()<\/li>\n\n\n\n
    • default equals compares high and low<\/li>\n\n\n\n
    • default hashcode<\/li>\n\n\n\n
    • default toString() which will output – HighLow[high=10, low=5]<\/li>\n<\/ul>\n\n\n\n
      “Record” is a class, it can be instantiated and used just like a class,<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      HighLow<\/span> <\/span>hl<\/span> <\/span>=<\/span> <\/span>new<\/span> <\/span>HighLow<\/span>(<\/span>10<\/span>,<\/span> <\/span>5<\/span>)<\/span>;<\/span><\/span>\nSystem<\/span>.<\/span>out<\/span>.<\/span>println<\/span> <\/span>(<\/span> <\/span>hl<\/span>.<\/span>high<\/span>())<\/span>;<\/span> <\/span>\/\/Output: 10<\/span><\/span>\nSystem<\/span>.<\/span>out<\/span>.<\/span>println<\/span> <\/span>(<\/span> <\/span>hl<\/span>.<\/span>low<\/span>())<\/span>;<\/span> <\/span>\/\/ Output: 5<\/span><\/span>\nSystem<\/span>.<\/span>out<\/span>.<\/span>println<\/span> <\/span>(<\/span> hl<\/span>)<\/span>;<\/span> <\/span>\/\/ Output: HighLow[high=10, low=5]<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
      Note, to access the member variable there is no \u201cget\u201d prefix like getHigh, it is accessed by hl.high() and hl.low(). Additionally, as all the member variables are immutable (implicitly final), there are no setters.<\/strong><\/p>\n\n\n\n
      More on Record<\/h2>\n\n\n\n
      As mentioned before, a record is a final class with member variables as final, hence there are no setters and there can be no additional member variables apart from what is mentioned as part of record declaration.<\/p>\n\n\n\n
      For example, the below is invalid<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      public<\/span> <\/span>record<\/span> HighLow<\/span>(<\/span>int<\/span> high<\/span>,<\/span> <\/span>int<\/span> low<\/span>)<\/span> <\/span>{<\/span><\/span>\n     <\/span>int<\/span> <\/span>diff<\/span>;<\/span> <\/span>\/\/COMPILATION ERROR<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
      Constructors in record<\/h2>\n\n\n\n
      Like in class, record can also have additional constructors however all of them will have to end up calling the constructor which takes all member variables in it, in the declared order.
      Say, for example, we wanted to take only high and default low to zero, then we add an additional constructor like the below,<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      public<\/span> <\/span>record<\/span> HighLow<\/span>(<\/span>int<\/span> high<\/span>,<\/span> <\/span>int<\/span> low<\/span>)<\/span> <\/span>{<\/span><\/span>\n    <\/span>public<\/span> <\/span>HighLow<\/span>(<\/span>int<\/span> <\/span>high<\/span>)<\/span> <\/span>{<\/span><\/span>\n      <\/span>this<\/span>(<\/span>high<\/span>,<\/span> <\/span>0<\/span>)<\/span>;<\/span><\/span>\n    <\/span>}<\/span><\/span>\n}<\/span><\/span>\n<\/span>\npublic<\/span> <\/span>class<\/span> <\/span>RecordDemo<\/span> <\/span>{<\/span><\/span>\n   <\/span>public<\/span> <\/span>static<\/span> <\/span>void<\/span> <\/span>main<\/span>(<\/span>String<\/span> <\/span>args<\/span>[])<\/span> <\/span>{<\/span><\/span>\n       <\/span>HighLow<\/span> <\/span>hl<\/span> <\/span>=<\/span> <\/span>new<\/span> <\/span>HighLow<\/span>(<\/span>100<\/span>)<\/span>;<\/span> <\/span>\/\/Low will be zero<\/span><\/span>\n       <\/span>HighLow<\/span> <\/span>hl2<\/span> <\/span>=<\/span> <\/span>new<\/span> <\/span>HighLow<\/span>(<\/span>100<\/span>,<\/span> <\/span>10<\/span>)<\/span>;<\/span> <\/span><\/span>\n       <\/span><\/span>\n   <\/span>}<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
      Additionally, if we require to validate the input values before setting it to the member variable, it can be done as follows,<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      public<\/span> <\/span>record<\/span> HighLow<\/span>(<\/span>int<\/span> high<\/span>,<\/span> <\/span>int<\/span> low<\/span>)<\/span> <\/span>{<\/span><\/span>\n  <\/span>public<\/span> <\/span>HighLow<\/span> <\/span>{<\/span> <\/span>\/\/This is a constructor, assume that both high and low are input to this.<\/span><\/span>\n      <\/span>if<\/span> <\/span>(<\/span>high <\/span><<\/span> low <\/span>)<\/span> <\/span>throw<\/span> <\/span>new<\/span> <\/span>RuntimeException<\/span>(<\/span>"<\/span>high must be greater than low<\/span>"<\/span>)<\/span>;<\/span><\/span>\n  <\/span>}<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
      As we can note above, the constructor declaration is quite different from the normal class. record constructor has the “access modifier” followed by the class name but does not take in any arguments. Although not explicitly stated, it is implicit that the above constructor takes two arguments high and low and those arguments can be directly used in the constructor block to perform any validation. Another magic that happens here, is that although not explicitly clear, after the validation and end of the return, high and low are assigned to the corresponding member\/instance variables this.high and this.low. However, we cannot explicitly set it in the constructor.<\/p>\n\n\n\n
      Similarly, record can also have methods like a class,<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      public<\/span> <\/span>record<\/span> HighLow<\/span>(<\/span>int<\/span> high<\/span>,<\/span> <\/span>int<\/span> low<\/span>)<\/span> <\/span>{<\/span>\t\t<\/span><\/span>\n    <\/span>public<\/span> <\/span>int<\/span> <\/span>diff<\/span>()<\/span> <\/span>{<\/span><\/span>\n      <\/span>return<\/span> high <\/span>-<\/span> low<\/span>;<\/span><\/span>\n    <\/span>}<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nHighLow<\/span> <\/span>hl<\/span> <\/span>=<\/span> <\/span>new<\/span> <\/span>HighLow<\/span>(<\/span>10<\/span>,<\/span> <\/span>5<\/span>)<\/span>;<\/span><\/span>\nint<\/span> <\/span>difference<\/span> <\/span>=<\/span> <\/span>hl<\/span>.<\/span>diff<\/span>()<\/span>;<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
       Records are Named Tuples<\/h2>\n\n\n\n
      Record is Named Tuple which are better than Generic Tuples that are generally accessed as \u201ctuple.left() and tuple.right()\u201d.<\/p>\n\n\n\n
      Generic tuple does not really convey meaning clearly as the method names are always tuple.left()\/right() or first()\/second().
      Instead in the above, it is easy to create a record and use them as hl.high() and low(), which explicitly states the purpose clearly. As we can see from the below example, we can return a Pair<int, int> but it does not express itself on what are <int, int> in a pair and whether the first int is low or the second int is low. Alternatively, returning HighLow clearly expresses itself and also can be accessed via highLow.high()\/low(). <\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      \/\/Example<\/span><\/span>\npublic<\/span> <\/span>Pair<\/span><int<\/span>,<\/span> <\/span>int><\/span> <\/span>getPair<\/span>()<\/span> <\/span>{<\/span><\/span>\n    <\/span>return<\/span> <\/span>new<\/span> <\/span>Pair<\/span><>(<\/span>10<\/span>,<\/span> <\/span>5<\/span>)<\/span>;<\/span><\/span>\n}<\/span><\/span>\nrecord<\/span> HighLow<\/span>(<\/span>int<\/span> high<\/span>,<\/span> <\/span>int<\/span> low<\/span>)<\/span> <\/span><\/span>\n<\/span>\nHighLow getHighLow() <\/span>{<\/span><\/span>\n    return new <\/span>HighLow<\/span>(<\/span>10<\/span>,<\/span>5<\/span>)<\/span>;<\/span><\/span>\n}<\/span> <\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
      How does record look internally?<\/h2>\n\n\n\n
      java.lang.Record is an abstract class that all record class implicitly extends.<\/p>\n\n\n\n
      For example, let us consider the below record<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      package<\/span> <\/span>com<\/span>.<\/span>example<\/span>.<\/span>demo<\/span>;<\/span><\/span>\npublic<\/span> <\/span>record<\/span> HighLow<\/span>(<\/span>int<\/span> high<\/span>,<\/span> <\/span>int<\/span> low<\/span>)<\/span> <\/span>{<\/span> <\/span>}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
      A simple record class mentioned above compiles to class and its internal structure can be seen below when you run “javap -p com.example.demo.HighLow”<\/p>\n\n\n\n
      <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
      public<\/span> <\/span>final<\/span> <\/span>class<\/span> <\/span>com<\/span>.example.demo.HighLow <\/span>extends<\/span> java.lang.<\/span>Record<\/span> <\/span>{<\/span><\/span>\n  <\/span>private<\/span> <\/span>final<\/span> <\/span>int<\/span> <\/span>high<\/span>;<\/span><\/span>\n  <\/span>private<\/span> <\/span>final<\/span> <\/span>int<\/span> <\/span>low<\/span>;<\/span><\/span>\n  <\/span>public<\/span> com.example.demo.<\/span>HighLow<\/span>(<\/span>int<\/span>,<\/span> <\/span>int<\/span>)<\/span>;<\/span><\/span>\n  <\/span>public<\/span> <\/span>int<\/span> <\/span>high<\/span>()<\/span>;<\/span><\/span>\n  <\/span>public<\/span> <\/span>int<\/span> <\/span>low<\/span>()<\/span>;<\/span><\/span>\n  <\/span>public<\/span> <\/span>final<\/span> <\/span>java<\/span>.<\/span>lang<\/span>.<\/span>String<\/span> <\/span>toString<\/span>()<\/span>;<\/span><\/span>\n  <\/span>public<\/span> <\/span>final<\/span> <\/span>int<\/span> <\/span>hashCode<\/span>()<\/span>;<\/span><\/span>\n  <\/span>public<\/span> <\/span>final<\/span> <\/span>boolean<\/span> <\/span>equals<\/span>(<\/span>java<\/span>.<\/span>lang<\/span>.<\/span>Object<\/span>)<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
      As we can note, record HighLow translates to a final class that extends java.lang.Record.
      From the above, we can also understand that<\/p>\n\n\n\n