Explain the concept of contract conditions and their role in software engineering.

Design by Contract (DbC) is a software development methodology where interactions between system components are described as formal agreements or "contracts." Each contract specifies:

• Preconditions — conditions that must be true before a method or function is called.
• Postconditions — conditions guaranteed after the method executes.
• Invariants — conditions that must remain true throughout the object's lifecycle.

The role of contract conditions in software engineering is to increase code reliability and predictability, facilitate debugging and testing, and improve documentation and understanding of component interactions.

Example in Java using comments:

class Account {
    private double balance;

    // Invariant: balance >= 0

    // Precondition: amount > 0
    // Postcondition: balance increases by amount
    public void deposit(double amount) {
        if (amount <= 0) {
            throw new IllegalArgumentException("Amount must be positive");
        }
        balance += amount;
    }

    // Precondition: amount > 0 and amount <= balance
    // Postcondition: balance decreases by amount
    public void withdraw(double amount) {
        if (amount <= 0 || amount > balance) {
            throw new IllegalArgumentException("Invalid amount");
        }
        balance -= amount;
    }
}