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The Java Interview Handbook: 300+ Interview Questions

Raw vs. Generic Types

Explore the distinctions between raw and generic types in Java. Understand how raw types affect type safety and how to use generics and annotations to manage legacy code. This lesson helps you write safer Java applications by mastering generics and type inference.

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We often encounter legacy Java code that does not use the diamond operator or specify type parameters. These are known as raw types. While modern Java development strictly relies on generic types for safety, understanding raw types is critical for technical interviews and maintaining older codebases.

Let's explore how raw types behave and how we can apply generics effectively.

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What is a raw type?

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Why do raw types still exist in modern Java?

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What happens when we mix raw types with generic types?

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We can observe this behavior and the resulting lack of type safety using a ...

Java
class Printer<T> {
    T item;
    public Printer(T item) {
        this.item = item;
    }
    public void changeItem(T item) {
        this.item = item;
    }
    public void consolePrinter() {
        System.out.println(item.toString());
    }
}
class Demonstration {
    public static void main(String[] args) {
        Printer<Integer> integerPrinter = new Printer<>(5);
        Printer rawPrinter = new Printer("my string");
        
        Printer printer = integerPrinter;
        printer = rawPrinter;
        printer.changeItem("string item");
        printer.consolePrinter();
    }
}
...