Can you explain the concept of a contract in the context of programming or system development?

In programming, a contract is a set of rules and obligations that define the interaction between system components. It describes what one part of the program promises to do (for example, a method or interface), and what the other part can expect in response.

For example, in Java, an interface can be considered a contract: it defines methods that a class must implement, guaranteeing certain behavior. The contract includes:

• Preconditions (what must be true before calling a method)
• Postconditions (what is guaranteed after executing a method)
• Invariants (conditions that must always be true for an object)

This helps create reliable and predictable systems where components can interact without deep knowledge of each other's internals.