Java常量完全指南：从基础定义到高级应用的最佳实践

final double PI = 3.14159; final int MAX_RETRY_COUNT = 3;

final double PI = 3.14159; final int MAX_ITERATIONS = 1000;

public class Circle {

private final double radius;

public Circle(double radius) {
    this.radius = radius;
}

}

public enum OrderStatus {

PENDING, CONFIRMED, SHIPPED, DELIVERED, CANCELLED

}

public final class AppConstants {

private AppConstants() {} // 防止实例化

public static final class Database {
    public static final int MAX_CONNECTIONS = 50;
    public static final String URL = "jdbc:mysql://localhost:3306/app_db";
    public static final int QUERY_TIMEOUT = 30;
}

public static final class Cache {
    public static final long DEFAULT_EXPIRE = 3600L;
    public static final int MAX_SIZE = 10000;
}

public static final class Security {
    public static final int PASSWORD_MIN_LENGTH = 8;
    public static final int LOGIN_ATTEMPTS_LIMIT = 5;
}

}

public class PaymentService {

public boolean validateAmount(BigDecimal amount) {
    return amount.compareTo(new BigDecimal("0.01")) >= 0 
        && amount.compareTo(new BigDecimal("1000000")) <= 0;
}

}