关于static class和public static class的测试记录

关于static class和public static class的测试记录

事情的起因，在看spring源码的时候，经常能看到一个内部类，而且，内部类用static关键字修饰。如

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication
@Conditional(SpringBootAdminClientEnabledCondition.class)
@AutoConfigureAfter({ WebEndpointAutoConfiguration.class, RestTemplateAutoConfiguration.class,
		WebClientAutoConfiguration.class })
@EnableConfigurationProperties({ ClientProperties.class, InstanceProperties.class, ServerProperties.class,
		ManagementServerProperties.class })
public class SpringBootAdminClientAutoConfiguration {



	@Bean
	@ConditionalOnMissingBean
	public StartupDatemetadataContributor startupDatemetadataContributor() {
		return new StartupDatemetadataContributor();
	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnWebApplication(type = Type.SERVLET)
	@AutoConfigureAfter(DispatcherServletAutoConfiguration.class)
	public static class ServletConfiguration {

		@Bean
		@Lazy(false)
		@ConditionalOnMissingBean
		public ApplicationFactory applicationFactory(InstanceProperties instance, ManagementServerProperties management,
				ServerProperties server, ServletContext servletContext, PathMappedEndpoints pathMappedEndpoints,
				WebEndpointProperties webEndpoint, ObjectProvider> metadataContributors,
				DispatcherServletPath dispatcherServletPath) {
			return new ServletApplicationFactory(instance, management, server, servletContext, pathMappedEndpoints,
					webEndpoint,
					new CompositemetadataContributor(metadataContributors.getIfAvailable(Collections::emptyList)),
					dispatcherServletPath);
		}

	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnWebApplication(type = Type.REACTIVE)
	public static class ReactiveConfiguration {

		@Bean
		@Lazy(false)
		@ConditionalOnMissingBean
		public ApplicationFactory applicationFactory(InstanceProperties instance, ManagementServerProperties management,
				ServerProperties server, PathMappedEndpoints pathMappedEndpoints, WebEndpointProperties webEndpoint,
				ObjectProvider> metadataContributors) {
			return new DefaultApplicationFactory(instance, management, server, pathMappedEndpoints, webEndpoint,
					new CompositemetadataContributor(metadataContributors.getIfAvailable(Collections::emptyList)));
		}

	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnBean(RestTemplateBuilder.class)
	public static class BlockingRegistrationClientConfig {

		@Bean
		@ConditionalOnMissingBean
		public BlockingRegistrationClient registrationClient(ClientProperties client) {
			RestTemplateBuilder builder = new RestTemplateBuilder().setConnectTimeout(client.getConnectTimeout())
					.setReadTimeout(client.getReadTimeout());
			if (client.getUsername() != null && client.getPassword() != null) {
				builder = builder.basicAuthentication(client.getUsername(), client.getPassword());
			}
			return new BlockingRegistrationClient(builder.build());
		}

	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnBean(WebClient.Builder.class)
	@ConditionalOnMissingBean(RestTemplateBuilder.class)
	public static class ReactiveRegistrationClientConfig {

		@Bean
		@ConditionalOnMissingBean
		public ReactiveRegistrationClient registrationClient(ClientProperties client, WebClient.Builder webClient) {
			if (client.getUsername() != null && client.getPassword() != null) {
				webClient = webClient.filter(basicAuthentication(client.getUsername(), client.getPassword()));
			}
			return new ReactiveRegistrationClient(webClient.build(), client.getReadTimeout());
		}

	}

}

为什么要这么写？？？带着疑问，做了下测试。

package org.test.dog;

public class Dog {
	class A {
		private String p;

		public String getP() {
			return p;
		}

		public void setP(String p) {
			this.p = p;
		}
	}

	static class B {
		private String p;

		public String getP() {
			return p;
		}

		public void setP(String p) {
			this.p = p;
		}

	}

	public class C {
		private String p;

		public String getP() {
			return p;
		}

		public void setP(String p) {
			this.p = p;
		}
	}

	public static class D {
		private String p;

		public String getP() {
			return p;
		}

		public void setP(String p) {
			this.p = p;
		}
	}

	A a = new A();
	B b = new B();
	C c = new C();
	D d = new D();

}

测试的重点，分为两种，一是和 Dog同处一个包里的 InnerPackageTest，目的是为了测试Dog.A, Dog.B，因为它们没有使用public关键字。二是和Dog没有处在同一个包的里的 OutPackageTest。

内部测试类

package org.test.dog;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;


public class InnerPackageTest {

	private static Integer newline = 2;
	
	public static void main(String[] args) throws Exception, IllegalAccessException, IllegalArgumentException, InvocationTargetException, SecurityException {

		Dog a = new Dog();

		System.out.println("----------------- A测试开始");

		// new Dog.A(); //报错，编译不通过
		Dog.A a1 = a.new A();
		message("打印实例:", a1);
		message("构造器个数:", Dog.A.class.getConstructors().length);
		newline(newline);

		System.out.println("----------------- B测试开始");
		//
		Dog.B b = new Dog.B();
		b.setP("");
		message("构造器个数:", Dog.B.class.getConstructors().length);
		message("打印实例:", b);

		newline(newline);

		System.out.println("----------------- C测试开始");
		//
		Dog.C c = a.new C();
		message("打印实例:", c);
		// new Dog.C();// 报错
		message("构造器个数:", Dog.C.class.getConstructors().length);
		Constructor[] cs = Dog.C.class.getConstructors();
		for (int i = 0; i < cs.length; i++) {
			message("构造器的样子:", cs[i].toGenericString());
		}
		Object c2 = Dog.C.class.getConstructors()[0].newInstance(a);
		message("反射出来的对象", c2.toString());

		newline(newline);

		System.out.println("----------------- D测试开始");
		Dog.D d = new Dog.D();
		message("打印实例:", d);
		message("构造器个数:", Dog.D.class.getConstructors().length);
		cs = Dog.D.class.getConstructors();
		for (int i = 0; i < cs.length; i++) {
			message("构造器的样子:", cs[i].toGenericString());
		}
		Object d2 = Dog.D.class.getConstructors()[0].newInstance();
		message("反射出来的对象", d2.toString());
	}

	public static void message(Object... args) {
		for (int i = 0; i < args.length; i++) {
			System.out.print(args[i] + "t");
		}
		System.out.println();
	}

	public static void newline(int newline) {
		for (int i = 1; i <= newline; i++) {
			System.out.println();
		}
	}
}

输出的结果为

----------------- A测试开始
打印实例:	org.test.dog.Dog$A@61f8bee4	
构造器个数:	0	


----------------- B测试开始
构造器个数:	0	
打印实例:	org.test.dog.Dog$B@7b49cea0	


----------------- C测试开始
打印实例:	org.test.dog.Dog$C@887af79	
构造器个数:	1	
构造器的样子:	public org.test.dog.Dog$C(org.test.dog.Dog)	
反射出来的对象	org.test.dog.Dog$C@7fac631b	


----------------- D测试开始
打印实例:	org.test.dog.Dog$D@5b87ed94	
构造器个数:	1	
构造器的样子:	public org.test.dog.Dog$D()	
反射出来的对象	org.test.dog.Dog$D@6e0e048a	

 外部测试类

package org.test.cat;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

import org.test.dog.Dog;


public class OutPackageTest {

	private static Integer newline = 2;
	
	public static void main(String[] args) throws Exception, IllegalAccessException, IllegalArgumentException, InvocationTargetException, SecurityException {

		Dog a = new Dog();

		System.out.println("----------------- A测试开始");

		// new Dog.A(); //报错，编译不通过
//		Dog.A a1 = a.new A();// 报错，编译不通过
//		message("打印实例:", a1);
//		message("构造器个数:", Dog.A.class.getConstructors().length);
		newline(newline);

		System.out.println("----------------- B测试开始");
		//
//		Dog.B b = new Dog.B(); //报错，编译不通过
//		b.setP("");
//		message("构造器个数:", Dog.B.class.getConstructors().length);
//		message("打印实例:", b);

		newline(newline);

		System.out.println("----------------- C测试开始");
		//
		Dog.C c = a.new C();
		message("打印实例:", c);
		// new Dog.C();// 报错
		message("构造器个数:", Dog.C.class.getConstructors().length);
		Constructor[] cs = Dog.C.class.getConstructors();
		for (int i = 0; i < cs.length; i++) {
			message("构造器的样子:", cs[i].toGenericString());
		}
		Object c2 = Dog.C.class.getConstructors()[0].newInstance(a);
		message("反射出来的对象", c2.toString());

		newline(newline);

		System.out.println("----------------- D测试开始");
		Dog.D d = new Dog.D();
		message("打印实例:", d);
		message("构造器个数:", Dog.D.class.getConstructors().length);
		cs = Dog.D.class.getConstructors();
		for (int i = 0; i < cs.length; i++) {
			message("构造器的样子:", cs[i].toGenericString());
		}
		Object d2 = Dog.D.class.getConstructors()[0].newInstance();
		message("反射出来的对象", d2.toString());
	}

	public static void message(Object... args) {
		for (int i = 0; i < args.length; i++) {
			System.out.print(args[i] + "t");
		}
		System.out.println();
	}

	public static void newline(int newline) {
		for (int i = 1; i <= newline; i++) {
			System.out.println();
		}
	}
}

输出的结果为

----------------- A测试开始


----------------- B测试开始


----------------- C测试开始
打印实例:	org.test.dog.Dog$C@61f8bee4	
构造器个数:	1	
构造器的样子:	public org.test.dog.Dog$C(org.test.dog.Dog)	
反射出来的对象	org.test.dog.Dog$C@7b49cea0	


----------------- D测试开始
打印实例:	org.test.dog.Dog$D@887af79	
构造器个数:	1	
构造器的样子:	public org.test.dog.Dog$D()	
反射出来的对象	org.test.dog.Dog$D@7fac631b	

总结一下，学习到的内容。

1、内部类A，B，由于没有使用修饰符，则默认的范围为包级别，这一点不变。

2、内部类A，B，在同一个包里被引用的时候，不能直接new，而是要通过Dog的实例对象来new。通过获取到的构造器个数来看，数量为0，也证实了这一点。

3、内部类C，如果只加了public，而不是public static时，根据获取的造造器来看，是有一个Dog参数的，所以，内部类C，虽然有public关键字，也是不能直接new。

4、内部类D，是通过public static 关键字来修饰的，进一步观察构造器，和普通的类（一个文件一个类，且是public级的）没有任何区别，所以，能够在包外直接new。

5、不能用static修饰顶级类Dog，只有内部类可以为static。