CODEWITHSUNDEEP
java
user1698044
user1698044

Reputation: 41

Initializing data structures to constant values with mixed data types

Is there any way to initialize a data structure to constant values in Java? I've searched high and low and can't find any such technique. I specifically want to initialize a class which contains mixed data types, such as String and int.

class xyz {
      String a;
      int    b;
}

static final xyz example1 = { "string value", 42 };    // This doesn't work.

static final xyz[] example2 = { { "value a", 42 }, { "value b", 43 } };  // this also doesn't work

I can initialize arrays of String, even two-dimensional arrays of String, but for some reason I cannot initialize a record structure or an array of record structures. I do this routinely in Delphi and find it very difficult to live without this feature.

Okay, I've been programming for about 40 years, so I am not exactly a newbie. I need to know if something like this is possible. I do want the constant data embedded in my app, not read in from a file, and using assignment statements to set up the data kind of defeats the purpose of declaring them as constants (final).

Thanks for any suggestions or comments. I really would like to find a good solution to this problem as I have a lot of Pascal code to convert to Java and I don't want to have to redesign all the data structures.

Upvotes: 4

Views: 8463

Answers (4)

assylias
assylias

Reputation: 328735

If you don't want to use a constructor or a static block as proposed in other answers, you can use the double brace initialization syntax:

static final xyz example1 =
  new xyz() {{ a = "string value"; b = 42; }};

Note that it creates an anonymous class.
Your second example would look like:

static final xyz[] example1 = new xyz[] {
  new xyz() {{ a = "value a"; b = 42; }},
  new xyz() {{ a = "value b"; b = 43; }}
};

However, if you have access to the xyz class, adding a constructor that takes two parameters would be more readable and (slightly) more efficient.

Upvotes: 9

Amit Deshpande
Amit Deshpande

Reputation: 19185

You can use Enums for this

enum xyz {
    VALUE_A("value a", 42), VALUE_B("value b", 43);

    String a;
    int b;

    xyz(String str, int value) {
        a = str;
        b = value;
    }

    static EnumSet<xyz> bothValues = EnumSet.of(xyz.VALUE_A, xyz.VALUE_B);
}

Upvotes: 0

amit
amit

Reputation: 178481

You can either write a constructor xyz(String,int) or use the default constructor and initialize the values in a static block:

static final xyz example1 = new xyz();
static { 
  example1.a = "string value";
  example1.b = 42;
}

Note: you should have access to the fields in the initializing class.

Also note: if xyz is an inner class - you will probably need to declare it as static for the above code to work.

P.S. The java convention is using an upper case letter as the first letter in a class name, so it should probably be renamed to Xyz

Upvotes: 0

kosa
kosa

Reputation: 66657

One way is write constructor for xyz class to achieve what you want.

class xyz {
      String a;
      int    b;

         xyz(String tempStr, int tempInt)
              {
            this.a = tempStr;
            this.b = tempInt;
             }
}

static final xyz example1 = new xyz("String value",  42);

Upvotes: 3

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