Java Class Library's "Contracts for Java 'Framework Practice Guide
'Contracts for Java' Framework Practice Guide
introduction:
'Contracts for Java' is a framework for providing contract programming for Java class libraries.Contract programming is a software development method, which aims to improve the reliability and maintenance of the code by defining and checking the contract.In Java, the contract can be understood as the front conditions, rear conditions, and unchanging formula defined on the method or class.
This article will introduce how to use the 'Contracts for Java' framework in the Java code to achieve contract programming and provide relevant example code.
1. Installation and introduction framework
1. Download the jar package of the 'Contracts for Java' framework and add it to the class path of the Java project.
2. Introduce the contracts package in the Java class:
import com.contract4j5.contract.Contract;
import com.contract4j5.contract.Post;
import com.contract4j5.context.TestContext;
import com.contract4j5.enforcer.ContractEnforcer;
2. Definition contract
In the Java class, the contract can be defined by annotation.'Contracts for Java' framework provides multiple annotations, including:
-Contract: Define the beginning and end of the contract.
-PRE: The pre -conditions of the definition method.
-POST: The rear conditions of the definition method.
-Invariant: The invariance of the definition class.
The following is a sample code fragment, which shows how to define the contract in the Java class:
public class ExampleClass {
private int counter;
@Pre("!name.isEmpty() && age > 0")
@Post("result == age * 2")
public int calculateDoubleAge(String name, int age) {
counter++;
return age * 2;
}
@Invariant("counter >= 0")
public int getCounter() {
return counter;
}
}
In the above examples, the CalcularEd allowance method defines the front conditions and rear conditions.The front conditions are defined by the Pre -annotation, indicating the conditions that need to be met before the method calls.The rear conditions are defined by post annotation, indicating that the results after the method calls the conditions that need to be met.
The getCounter method defines the unable variable type.Use the Invariant annotation definition, indicating that the class must meet the conditions in any state.
3. Contract verification and execution
Through the 'Contracts for Java' framework, the contract can be verified during the test phase and the contract is executed during runtime.
The following is a sample code fragment that shows how to verify and execute the contract:
public class ExampleClassTest {
public static void main(String[] args) {
TestContext context = new TestContext();
ContractEnforcer enforcer = new ContractEnforcer();
context.setCurrentEnforcer(enforcer);
ExampleClass example = new ExampleClass();
// Verification contract
if (Contract.enforce()) {
// Execute code logic
System.out.println(example.calculateDoubleAge("John Doe", 30));
} else {
System.err.println ("Contract verification failed!");
}
}
}
In the above example, we created a TestContext object and then set it to the current contract as a actuator.We then created an example of ExampleClass and executed the Calculated allowance method after the verification contract was successful.
When the contract verification fails, we can capture the corresponding abnormalities and deal with it.
in conclusion:
By using the 'Contracts for Java' framework in the Java code, we can implement contract programming to improve the reliability and maintenance of the code.By defining and verifying the contract, we can better understand the methods and class behaviors and capture potential errors.
Please note that when using contract programming in actual projects, it is necessary to combine the actual needs and code specifications of the project for appropriate design and practice.
The above is a guide and example code about 'Contracts for Java' framework practice.It is hoped that this article can help readers understand and apply basic concepts and skills of contract programming.
