Built-in annotations
- Java course
- Advanced
- Lesson 31/82
- 5 min
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.
Practice 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.
Starter code
// Define the Product class
// Override the toString method
// Print to the screen in mainSample 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"));
}
}Expected output
Product: pen
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which annotation makes the compiler check that a method overrides a superclass method?
- @SuppressWarnings
- @Deprecated
- @Override Correct answer
- @FunctionalInterface
Explanation: @Override tells the compiler to compare the signature with the superclass.
2 Form the @Override marker
public class Animal {
@____
public String toString() { return "Animal"; }
}public class Animal {
@Override
public String toString() { return "Animal"; }
}Explanation: The @Override marker shows toString is overridden.
3 Match the built-in annotations
| Term | Meaning |
|---|---|
@Override |
Override check |
@Deprecated |
Deprecated marker |
@SuppressWarnings |
Warning suppression |
@FunctionalInterface |
Single abstract method |