How to use the 'Contracts for Java' framework in the Java class library for contract development
How to use the 'Contracts for Java' framework in the Java class library for contract development
Overview:
Contract -driven development is a software development methodology. By clearing the contract between the methods and the class, the reliability and maintenance of the code are increased.'Contracts for Java' is an open source framework for the Java class library, which provides a mechanism for verifying and mandating these contracts during runtime.This article will introduce how to use the 'Contracts for Java' framework in the Java library for contract development.
Step 1: Introduce 'Contracts for Java' framework
First, you need to introduce the 'Contracts for Java' framework in your Java project.You can achieve it by adding related dependencies in the construction configuration file of the project, or manually download and import jar files to achieve it.
Step 2: Define contracts
Next, you need to define contracts in your class and methods.The contract can be divided into three categories:
1. Preconditions: Define method calls before.
2. PostConditions: The constraints after the definition method is executed.
3. optional condition (Invariants): The definition method is always unchanged during the execution of the method.
You can use the annotations provided by the 'Contracts for Java' framework to define these contracts.For example,@Requires annotations are used to define front conditions,@ENSURES annotations are used to define rear conditions,@invariant annotations are used to define optional conditions.You can use these annotations above or method.
The following is a simple example. Demonstration of how to define the front conditions and rear conditions of a method using a contract:
public class ExampleClass {
public int addNumbers(@Requires("a >= 0") int a, @Requires("b >= 0") int b) {
return a + b;
}
@Ensures("result >= 0")
public int subtractNumbers(int a, int b) {
int result = a - b;
return result;
}
}
In the above example, the addnumbers method defines a front condition a> = 0 and b> = 0, and the Subtractnumbers method defines a rear conditionert> = 0.
Step 3: Enable contract verification
Before using the 'Contracts for Java' framework, you need to enable contract verification in your code.This can be implemented by setting the corresponding options in the project configuration file, or setting the system property when starting the application to set the system attribute.
The following is an example. The method of enabling contract verification in the Java application:
public class Main {
public static void main(String[] args) {
System.setProperty("java.contract.enabled", "true");
// your code here
}
}
You need to set this property before running your application.
Step 4: Compile and run code
You can compile and run your code when your code is set and defined a suitable contract.When running, the 'Contracts for Java' framework will meet these constraints based on the call and result of the defined contract verification method.
If necessary, the 'Contracts for Java' framework will throw the corresponding abnormalities to indicate which contract conditions violate.
Summarize:
Using the 'Contracts for Java' framework for contract -driven development can help you add the reliability and maintenance of code to the Java library.By defining the front conditions, rear conditions, and optional conditions, the contract between the methods and the class can be clearly defined.Through enabled contract verification, the 'Contracts for Java' framework will verify and enforce these contracts during runtime.This can help developers find and repair potential problems early, thereby improving the quality and reliability of the software.
