java - Allowing final fields to take default values -

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i writing parser binary file format. have created classes represent deserialized structures reading, in use final variables hold extracted data.

class myobject {     final int my_x;     final int my_y;     final int my_z; }

the bump running presence of fields depends on flags being set. example:

myobject(inputstream is) {     my_x = in.read();     if (my_x == 1) {         my_y = in.read();         if (my_y == 1) {             my_z = in.read();         }     } }

however, gives me error because my_y , my_z may not initialized. these conditionals can 5-6 levels deep, , don't want track fields may not read @ each level of branch tree. complication that, based on flags, there may subobjects handle same pattern top-level structures.

class myobject {     final int my_x;     final subobject my_subobject;      myobject(inputstream is) {         my_x = is.read();         if (my_x == 1)             my_subobject = new subobject(is);     }      class subobject {         final int sub_x;         final int sub_y;          subobject(inputstream is) {             sub_x = is.read();             if (sub_x == 1)                 sub_y = is.read();         }     } }

is there way make fields final without twisting code handle each possible combination of flags?

use local variables , assign final fields @ end of constructor.

public myobject(inputstream is) {     int x = default_x_value;     int y = default_y_value;     int z = default_z_value;     x = in.read();     if (x == 1) {         y = in.read();         if (y == 1) {             z = in.read();         }     }     my_x = x;     my_y = y;     my_z = z; }

alternatively (as jon skeet suggests in comment), use static factory method computes appropriate values no-default constructor:

public static myobject makemyobject(inputstream is) {     int x = default_x_value;     int y = default_y_value;     int z = default_z_value;     x = in.read();     if (x == 1) {         y = in.read();         if (y == 1) {             z = in.read();         }     }     return new myobject(x, y, z); }

a third approach define initializer object class:

public class myobject {     private static class myobjectinitializer {         int x = default_x_value;         int y = default_y_value;         int z = default_z_value;         myobjectinitializer(inputstream is) {             x = in.read();             if (x == 1) {                 y = in.read();                 if (y == 1) {                     z = in.read();                 }             }         }     }     public myobject(inputstream is) {         this(new myobjectinitializer(is));     }     private myobject(myobjectinitializer init) {         my_x = init.x;         my_y = init.y;         my_z = init.z;     } }

the initializer class may have utility on own, in case make (and corresponding myobject constructor) public.


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