Annotations and Reflection

Class Literal

A class literal gives a program a Class object without creating an instance.

class literal The `.class` syntax asks Java for metadata about a type.
Class object A Class object describes a type and exposes names, package data, methods, fields, and constructors.

Class Literal

choice
ClassLiteral.java
Replay: real traced execution (multi-file project)
public class ClassLiteral {
    public static void main(String[] args) {
        int choice = 1;
        Class<?> type;

        if (choice == 1) {
            type = String.class;
        } else if (choice == 2) {
            type = Integer.class;
        } else {
            type = Boolean.class;
        }

        System.out.println("simple=" + type.getSimpleName());
        System.out.println("package=" + type.getPackageName());
    }
}

public class ClassLiteral {
    public static void main(String[] args) {
        int choice = 2;
        Class<?> type;

        if (choice == 1) {
            type = String.class;
        } else if (choice == 2) {
            type = Integer.class;
        } else {
            type = Boolean.class;
        }

        System.out.println("simple=" + type.getSimpleName());
        System.out.println("package=" + type.getPackageName());
    }
}

public class ClassLiteral {
    public static void main(String[] args) {
        int choice = 3;
        Class<?> type;

        if (choice == 1) {
            type = String.class;
        } else if (choice == 2) {
            type = Integer.class;
        } else {
            type = Boolean.class;
        }

        System.out.println("simple=" + type.getSimpleName());
        System.out.println("package=" + type.getPackageName());
    }
}

  1. choice ← 1

    1public class ClassLiteral {2    public static void main(String[] args) {3        int choice→ 1 = 1;  //@choice=2, 34        Class<?> type;

  2. type ← class java.lang.String

    6if (choice1 == 1) {7    type→ class java.lang.String = String.class;8} else if (choice == 2) {

  3. System.out.println("simple=" + type.getSimpleName());

    14    System.out.println("simple=" + type.getSimpleName());15    System.out.println("package=" + type.getPackageName());16}
    outputsimple=String
package=java.lang

  1. choice ← 2

    1public class ClassLiteral {2    public static void main(String[] args) {3        int choice→ 2 = 2;4        Class<?> type;

  2. type ← class java.lang.Integer

    7    type = String.class;8} else if (choice2 == 2) {9    type→ class java.lang.Integer = Integer.class;10} else {

  3. System.out.println("simple=" + type.getSimpleName());

    14    System.out.println("simple=" + type.getSimpleName());15    System.out.println("package=" + type.getPackageName());16}
    outputsimple=Integer
package=java.lang

  1. choice ← 3

    1public class ClassLiteral {2    public static void main(String[] args) {3        int choice→ 3 = 3;4        Class<?> type;

  2. type ← class java.lang.Boolean

    9    type = Integer.class;10} else {11    type→ class java.lang.Boolean = Boolean.class;12}

  3. System.out.println("simple=" + type.getSimpleName());

    14    System.out.println("simple=" + type.getSimpleName());15    System.out.println("package=" + type.getPackageName());16}
    outputsimple=Boolean
package=java.lang