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Home Java javaTutorial Raw types and legacy code

Raw types and legacy code

Jan 03, 2025 pm 09:03 PM

Tipos brutos e código legado

raw types were introduced to allow compatibility between legacy (pre-generic) codes and the generics introduced in JDK 5. They allow for gradual transition, but compromise type safety.

Definitions and Features
Raw type:

  • Use a generic class without specifying type arguments. Example:
Gen raw = new Gen(new Double(98.6)); // Tipo bruto criado

Compatibility:

Raw type variables can receive any generic object and vice versa.
There is no compile-time type checking, resulting in possible run-time errors.

Code Example

// Classe Gen com suporte a genéricos
class Gen<T> {
    T ob; // Declara um objeto do tipo T

    Gen(T o) { // Construtor
        ob = o;
    }

    T getob() { // Retorna o objeto ob
        return ob;
    }
}

// Demonstra??o de tipos brutos
class RawDemo {
    public static void main(String[] args) {
        // Usando genéricos corretamente
        Gen<Integer> iOb = new Gen<>(88);
        Gen<String> strOb = new Gen<>("Generics Test");

        // Criando um tipo bruto
        Gen raw = new Gen(new Double(98.6));
        double d = (Double) raw.getob(); // Funciona, mas perde seguran?a de tipos
        System.out.println("value: " + d);

        // Erros de tempo de execu??o com tipos brutos
        // int i = (Integer) raw.getob(); // Erro de tempo de execu??o!

        // Atribui??o de tipo bruto para genérico
        strOb = raw; // Correto, mas perigoso
        // String str = strOb.getob(); // Erro de tempo de execu??o!

        // Atribui??o de genérico para tipo bruto
        raw = iOb; // Correto, mas perigoso
        // d = (Double) raw.getob(); // Erro de tempo de execu??o!
    }
}

Risks of Using Raw Types
Lack of Type Safety:

  • Assigning raw types to generics or vice versa can cause runtime errors.

Examples:

strOb = raw; // Perigoso: raw contém Double, mas strOb espera String
raw = iOb; // Perigoso: raw agora contém Integer, mas coer??o pode falhar

Runtime Exceptions:

There is no way to detect inconsistencies at compile time.
Example:

int i = (Integer) raw.getob(); // Erro porque raw contém Double

Non-Verification Warnings:

  • The javac compiler generates warnings when it detects raw types used in an unsafe way.

Examples that generate warnings

Gen raw = new Gen(new Double(98.6)); // Tipo bruto
strOb = raw; // Atribui??o insegura

Recommendations
Avoid using raw types:

  • Always use type arguments to take advantage of the safety offered by generics.

Example:

Gen<Integer> iOb = new Gen<>(88); // Correto e seguro

Treat legacy code with care:

  • Add rigorous checks and tests when integrating pre-generic code with generics.

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