鏈式編程

1、鏈式編程在StringBulider中的使用

（1）鏈式編程的使用

@SpringBootTest
@RunWith(SpringRunner.class)
public class MyTest {
    private Logger log = Logger.getLogger("test");
    @Test
    public void StringBuliderTest(){
       StringBuilder stringBuilder=new StringBuilder().append("1").append("2").append(3).append(4);
       log.info(stringBuilder.toString());
    }
}

2021-01-20 17:18:00.733  INFO 8376 --- [           main] test                                     : 1234

鏈式編程的寫法能夠使代碼更加簡潔可讀性強

（2）源碼

StringBulider：

  @Override
    public StringBuilder append(String str) {
        super.append(str);
        return this;
    }

StringBulider的父類：AbstractStringBuilder

 public AbstractStringBuilder append(String str) {
        if (str == null)
            return appendNull();
        int len = str.length();
        ensureCapacityInternal(count + len);
        str.getChars(0, len, value, count);
        count += len;
        return this;
    }

就是把拼接后的字符串返回

 

2、應用方法

（1）定義一個學生類

public class Student {
    private String name;
    private int age;
    private String address;

    public Student setName(String name) {
        this.name = name;
        return this;
    }

    public Student setAge(int age) {
        this.age = age;
        return this;
    }

    public Student setAddress(String address) {
        this.address = address;
        return this;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public String getAddress() {
        return address;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", address='" + address + '\'' +
                '}';
    }
}

return的是this，返回的是當前對象的引用(實際調用這個方法的實例化對象)

（2）測試

   @Test
    public void testStudent(){
        Student student=new Student().setName("tom").setAge(12).setAddress("河南");
        log.info(student.toString());
    }

2021-01-20 19:17:59.471  INFO 13508 --- [           main] test                                     : Student{name='tom', age=12, address='河南'}

（3）還可以這樣寫

public class Student {
    private static Student student;
    private String name;
    private int age;
    private String address;

    public static Student Student() {
        student=new Student();
        return student;
    }

    public Student setName(String name) {
        student.name = name;
        return student;
    }

    public Student setAge(int age) {
        student.age = age;
        return student;
    }

    public Student setAddress(String address) {
        student.address = address;
        return student;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public String getAddress() {
        return address;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", address='" + address + '\'' +
                '}';
    }
}

測試：

  @Test
    public void testStudent(){
        Student.Student().setName("tom").setAge(12).setAddress("河南");
    }

 

3、Lombok中的鏈式編程

（1）需要添加注解@Accessors(chain = true)

@Getter
@Setter
@ToString
@Accessors(chain = true)
public class Student {
    private static Student student;
    private String name;
    private int age;
    private String address;
}

測試：

  @Test
    public void testStudent(){
        Student student=new Student().setName("tom").setAge(12).setAddress("河南");
        log.info(student.toString());
    }

2021-01-20 19:45:15.780  INFO 3048 --- [           main] test                                     : Student(name=tom, age=12, address=河南)