how to generate symbol Class<?> with javapoet

Question

i want to generate a field like this:

public static Map<String, Class<?>> ID_MAP = new HashMap<String, Class<?>>();

WildcardTypeName.subtypeOf(Object.class) can give '?' WildcardTypeName.subtypeOf(Class.class) can give 'Class'

Answer 1

If you break down that type into its component parts you get:

• ?
• Class
• Class<?>
• String
• Map
• Map<String, Class<?>>

You can then build up these component parts in the same way using JavaPoet's APIs:

• TypeName wildcard = WildcardTypeName.subtypeOf(Object.class);
• TypeName cls = ClassName.get(Class.class);
• TypeName clsWildcard = ParameterizedTypeName.create(cls, wildcard);
• TypeName string = ClassName.get(String.class);
• TypeName map = ClassName.get(Map.class);
• TypeName mapStringClass = ParameterizedTypeName.create(map, string, clsWildcard);

Once you have that type, doing the same for HashMap should be easy (just replace Map.class with HashMap.class) and then building the field can be done like normal.

FieldSpec.builder(mapStringClass, "ID_MAP")
    .addModifiers(PUBLIC, STATIC)
    .initializer("new $T()", hashMapStringClass)
    .build();