Built-in annotations

Learn built-in annotations @Override and @Deprecated.

Built-in annotations

The Java compiler predefines several annotations (markers). They do not change behavior but give the compiler hints and catch mistakes early.

Three core built-ins: @Override checks that a method overrides a superclass method; @Deprecated marks an element that should no longer be used; @SuppressWarnings silences selected warnings. Each starts with @ and is placed just above the modifier.

Silencing warnings with @SuppressWarnings

@SuppressWarnings turns off specific warning kinds. Common values: "unchecked" for raw types, "deprecation" for old API use, "unused" for unused variables.

Example: @SuppressWarnings("unchecked") above a method hides unchecked warnings in that method. It is good practice to suppress at the narrowest scope; apply it to a single method rather than the whole class.

Exercise Write toString with @Override

Define a Product class with a name field and a constructor. Mark the toString method with @Override and return "Product: " + name. In main, create a product and print it with System.out.println.

Show example solution

public class Product {
    private String name;
    public Product(String name) { this.name = name; }
    @Override
    public String toString() { return "Product: " + name; }
    public static void main(String[] args) {
        System.out.println(new Product("pen"));
    }
}

Test yourself

Which annotation makes the compiler check that a method overrides a superclass method?
- @SuppressWarnings
- @Deprecated
- @Override
- @FunctionalInterface
Show answer

@Override — @Override tells the compiler to compare the signature with the superclass.

Form the @Override marker

public class Animal {
    @____
    public String toString() { return "Animal"; }
}

Show answer

public class Animal {
    @Override
    public String toString() { return "Animal"; }
}

Match the built-in annotations

@Override

Override check
@Deprecated

Deprecated marker
@SuppressWarnings

Warning suppression
@FunctionalInterface

Single abstract method

Next lesson: @interface

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