1.枚举(enum)

枚举是一组常量的集合，里面包含一组有限的特定的对象，通常全部大写。

自定义枚举类型

1. 构造器私有化
2. 类内部创建一组对象，使用public static final修饰
3. 提供get方法，不提供set方法

package enmu;

public class Enmu01 {
          
   
    public static void main(String[] args) {
          
   
        System.out.println(Enum01_.E1);//Enum01_{a=1}
        System.out.println(Enum01_.E1.getA());//1
    }
}
class Enum01_{
          
   
    private int a;
    public static final Enum01_ E1 = new Enum01_(1);

    private Enum01_(int a) {
          
   
        this.a = a;
    }

    public int getA() {
          
   
        return a;
    }

    @Override
    public String toString() {
          
   
        return "Enum01_{" +
                "a=" + a +
                };
    }
}

enum

1. class变enum
2. 定义的常量类型在最前面
3. 多个常量用,分割
4. 无参构造可以省略()
5. 枚举类默认继承Enum类，所以不能继承其他类，可以实现接口
6. E1(1), E2(2), E3是对象
7. 默认toString返回常量名

package enmu;

public class Enmu01 {
          
   
    public static void main(String[] args) {
          
   
        System.out.println(Enum01_.E1);//Enum01_{a=1}
        System.out.println(Enum01_.E2);//Enum01_{a=2}
        System.out.println(Enum01_.E1.getA());//1
        System.out.println(Enum01_.E2.getA());//2
    }
}

enum Enum01_ {
          
   
    //1.class变enum
    //2.定义的常量类型在最前面
    //3.多个常量用,分割
    //4.无参构造可以省略()
    E1(1), E2(2), E3;
    private int a;

    Enum01_() {
          
   
    }

    private Enum01_(int a) {
          
   
        this.a = a;
    }

    public int getA() {
          
   
        return a;
    }

    @Override
    public String toString() {
          
   
        return "Enum01_{" +
                "a=" + a +
                };
    }
}

2.注解

@interface注解类

修饰注解的注解是元注解

1. Retention 指定注解的作用范围
2. Target 指定注解的使用地方
3. Documented 指定注解是否在Javadoc体现
4. Inherited 子类会继承父类注解

@Override重写方法的注解，重写了父类编译通过，没有重写报错。只能用于方法，因为@Target(ElementType.METHOD)

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.SOURCE)
public @interface Override {
          
   
}

@Deprecated表示某个元素已过时，新旧版本的过渡

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(value={
          
   CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE})
public @interface Deprecated {
          
   
}

@SuppressWarnings抑制警告，传入一个数组

@Target({
          
   TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE})
@Retention(RetentionPolicy.SOURCE)
public @interface SuppressWarnings {
          
   
    /**
     * The set of warnings that are to be suppressed by the compiler in the
     * annotated element.  Duplicate names are permitted.  The second and
     * successive occurrences of a name are ignored.  The presence of
     * unrecognized warning names is <i>not</i> an error: Compilers must
     * ignore any warning names they do not recognize.  They are, however,
     * free to emit a warning if an annotation contains an unrecognized
     * warning name.
     *
     * <p> The string {@code "unchecked"} is used to suppress
     * unchecked warnings. Compiler vendors should document the
     * additional warning names they support in conjunction with this
     * annotation type. They are encouraged to cooperate to ensure
     * that the same names work across multiple compilers.
     * @return the set of warnings to be suppressed
     */
    String[] value();
}

ross multiple compilers. * @return the set of warnings to be suppressed */ String[] value(); }