重构: 使用替换丑陋的if else代码

使用Enum替换int常量

这一步比较简单，先创建一个enum类

package de.jingge.refactoring;

public enum SystemState {

    LOGGEDIN,

    LOGGEDOUT,

    IDLE;

}

然后开始重构SystemManager, 使用SystemState代替SystemManager里的int状态：

   1. 添加 import static de.jingge.refactoring.SystemState.*;
   2. 删除所有的integer常量  
   3. 将变量state的类型改为SystemState.

代码如下：

package de.jingge.refactoring;

import static de.jingge.refactoring.SystemState.*;

public class SystemManager {

    SystemState state;

    public void login() {
        // call service#login()
        updateState(LOGGEDIN);
    }
   
    public void logout() {
        // call service#logout()
        updateState(LOGGEDOUT);
    }
   
    public void idle() {
        // call some other services
        updateState(IDLE);
    }
   
    public void updateState(SystemState state) {
        if (state == LOGGEDIN) {
            // do something after logging in is successful,
            // for example: show welcome dialog, open the last edit document, etc.
        } else if (state == LOGGEDOUT) {
            // do something after logging out is successful,
            // for example: free used resource, dispose GUI components, etc.
        } else if (state == IDLE) {
            // do something after the user is idle,
            // for example: save the application state temporarily, lock the application, etc.
        } else {
            throw new IllegalArgumentException("unknown state");
        }
        this.state = state;
    }
}

然后重构测试类:

1.    添加import static de.jingge.refactoring.SystemState.*;
2.    删除所有常量前引用的SystemManager.

package de.jingge.refactoring;

import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
import static org.junit.Assert.*;
import static de.jingge.refactoring.SystemState.*;


public class SystemManagerTest {

    private static SystemManager manager;

    @BeforeClass
    public static void setUpClass() throws Exception {
        manager = new SystemManager();
        // add some service mock objects
    }
   
    @AfterClass
    public static void tearDownClass() throws Exception {
    }
   
    @Test
    public void login() {
        manager.login();
        assertEquals(manager.state, LOGGEDIN);
    }
  
    @Test
    public void logout() {
        manager.logout();
        assertEquals(manager.state, LOGGEDOUT);
    }

    @Test
    public void idle() {
        manager.idle();
        assertEquals(manager.state, IDLE);
    }
}

运行这个测试类->通过