Type

Posted 2021-02-21 kikochz

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了Type相关的知识，希望对你有一定的参考价值。

/**

Type is the common superinterface for all types in the Java
programming language. These include raw types, parameterized types,
array types, type variables and primitive types.
@since 1.5
/
public interface Type {
/*
- Returns a string describing this type, including information
- about any type parameters.
- @implSpec The default implementation calls {@code toString}.
- @return a string describing this type
- @since 1.8
  */
  default String getTypeName() {
  return toString();
  }
  }
  上面是在JDK1.8中Type类的源代码。

Type是Java语言中所有类型的父接口，包括
raw types(原始类型，包括类，枚举，接口，注解，数组（但不包括泛型数组）),
parameterized types（参数化类型，如Set,Map<String,String>,Class<?>）,
array types(泛型数组和参数类型数组，如T[],List[]),
type variables(类型变量，如T，K，V) and
primitive types（基本类型，如boolean,char,byte,short,int,long,float,double）.

继承图

image.png
每种类型都有对应的类或者接口

raw types 对应 Class

parameterized types 对应 ParameterizedType

array types 对应 GenericArrayType

type variables 对应 TypeVariable

primitive types 对应 Class

还有一种是通配符？
? 对应 WildcardType

下面看一下简单的例子吧

声明一个枚举类

package com.type;

public enum EnumTest {
}
声明一个接口类

package com.type;

public interface InterfaceTest {
}
声明一个注解类

package com.type;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface AnnotationTest {
}
package com.type;

import java.util.List;
import java.util.Map;

public class TypeBean {
private T t;
private String string;
private Map<String,String> map;
private List list;
private int aint;
private T[] tArray;
private int[] intAarry;
private Integer[] integers;
private List[] lists;
private Class<?> clazz;
private EnumTest enumTest;
private InterfaceTest interfaceTest;
private AnnotationTest annotationTest;
}
测试类

package com.type;

import java.lang.reflect.*;

public class TypeBeanTest {
public static void main(String[] args) {
Field[] declaredFields = TypeBean.class.getDeclaredFields();
for (int i = 0; i < declaredFields.length; i++) {
Field declaredField = declaredFields[i];
Type genericType = declaredField.getGenericType();
System.out.println("变量名：" + declaredField.getName());
System.out.println("变量声明的类型："+genericType.getTypeName());
if (genericType instanceof Class) {
System.out.println("变量类型为Class");
} else if (genericType instanceof ParameterizedType) {
System.out.println("变量类型为ParameterizedType");
} else if (genericType instanceof TypeVariable) {
System.out.println("变量类型为TypeVariable");
} else if (genericType instanceof GenericArrayType) {
System.out.println("变量类型为GenericArrayType");
} else if (genericType instanceof WildcardType) {
System.out.println("变量类型为WildcardType");
}
System.out.println();
}
}
}
测试结果