从Java到Golang快速入门

从Java到Golang快速入门

Golang从09年发布,中间经历了多个版本的演进,已经渐渐趋于成熟,并且出现了很多优秀的开源项目,比如我们熟知的docker,etcd,kubernetes等,其媲美于C的性能、Python的开发效率,又被称为21世纪的C语言,尤其适合开发后台服务。这篇文章主要是介绍Golang的一些主要特性,和Java做一个对比,以便更好的理解Golang这门语言。

关于Golang环境的搭建就不讲了,可以参考官方文档或者Google一下,配置下SDK和PATH即可,非常简单,我们就从Go版本的Hello World开始

Hello World

每种语言都有自己的Hello World,Go也不例外,Go版本的如下:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n11" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">package mainimport "fmt"func main() {

fmt.Println("Hello, 世界")

}</pre>

我们使用go run运行后,会在控制台终端看到 Hello, 世界
的输出。我们来看下这段代码

  1. package 是一个关键字,定义一个包,和Java里的package一样,也是模块化的关键。

  2. main包是一个特殊的包名,它表示当前是一个可执行程序,而不是一个库。

  3. import 也是一个关键字,表示要引入的包,和Java的import关键字一样,引入后才可以使用它。

  4. fmt是一个包名,这里表示要引入fmt这个包,这样我们就可以使用它的函数了。

  5. main函数是主函数,表示程序执行的入口,Java也有同名函数,但是多了一个String[]类型的参数

  6. Println是fmt包里的函数,和Java里的system.out.println作用类似,这里输出一段文字。

整段代码非常简洁,关键字、函数、包等和Java非常相似,不过注意,go是不需要以;(分号)结尾的。

变量

go语言变量的声明和java的略有不同,以声明一个int类型,变量名为age为例,go语言变量生成如下:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n38" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

var age int =10</pre>

同样的变量,在java中的声明是:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n41" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

int age = 10;</pre>

可以看到go的变量声明,修饰变量的类型在变量的后面,而且是以var关键字开头。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n44" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

var 变量名 类型 = 表达式</pre>

最后面的赋值可以在声明的时候忽略,这样变量就有一个默认的值,称之为 零值
零值
是一个统称,以类型而定,比如int类型的零值为0,string类型的零值是””空字符串。

在go中除了以var声明变量之外,还有一种简短的变量声明方式:=,比如上面例子,可以如下简单声明:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n49" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

age := 10</pre>

这种方式和上面的例子等价,但是少了var和变量类型,所以简短方便,用的多。使用这种方式,变量的类型由go根据值推导出来,比如这里默认是int。

常量

有了变量,就少不了常量,和var关键字不一样,go的常量使用const声明,这个和C里的常量一样。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n55" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

const age = 10</pre>

这样就声明了一个常量age,其值是10,因为我们这里没有指定常量的类型,所以常量的类型是根据值推导出来的。所以等价的我们也可以指定常量类型,如下:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n58" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

const age int = 10</pre>

相比来说,java下的常量定义就要复杂一些,要有static final修饰符,才是常量:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n61" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

private static final int AGE = 10;</pre>

这个和go的实现等价,但是它的定义修饰符比go多多了,而且常量类型不能省略。

大小写标记访问权限

我们上面的go例子中我特意用了小些的变量名age,甚至常量我也没有写成AGE,但是在java中,对于常量我们的习惯是全部大些。

在go中不能随便使用大小写的问题,是因为大小写具有特殊意义,在go中,大些字母开头的变量或者函数等是public的,可以被其他包访问;小些的则是private的,不能被其他包访问到。这样就省去了public和private声明的烦恼,使代码变的更简洁。

特别说明,这些导出规则只适用于包级别名字定义,不能使函数内部的定义。

包的规则和java很像,每个包都有自己独立的空间,所以可以用来做模块化,封装,组织代码等。和java不同的是,go的包里可以有函数,比如我们常用的fmt.Println(),但是在在java中没有这种用法,java的方法必须是属于一个类或者类的实例的。

要使用一个包,就需要先导入,使用import关键字,和java也一样,可以参见前面的helloworld示例。

如果我们需要导入多个包的时候,可以像java一样,一行行导入,也可以使用快捷方式一次导入,这个是java所没有的。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n79" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

import ( "io"

"log"

"net"

"strconv")</pre>

类型转换

go对于变量的类型有严格的限制,不同类型之间的变量不能进行赋值、表达式等操作,必须要要转换成同一类型才可以,比如int32和int64两种int类型的变量不能直接相加,要转换成一样才可以。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n83" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;"> var a int32 = 13

var b int64 = 20

c := int64(a) + b</pre>

这种限制主要是防止我们误操作,导致一些莫名其妙的问题。在java中因为有自动转型的概念,所以可以不同类型的可以进行操作,比如int可以和double相加,int类型可以通过 +
和字符串拼接起来,这些在go中都是不可行的。

map

map类型,Java里是Map接口,go里叫做字典,因为其常用,在go中,被优化为一个语言上支持的结构,原生支持,就像一个关键字一样,而不是java里的要使用内置的sdk集合库,比如HashMap等。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n89" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

ages := make(map[string]int)

ages["linday"] = 20

ages["michael"] = 30

fmt.Print(ages["michael"])</pre>

go里要创建一个map对应,需要使用关键字make,然后就可以对这个map进行操作。

map的结构也非常简单,符合KV模型,定义为map[key]value, 方括号里是key的类型,方括号外紧跟着对应的value的类型,这些明显和Java的Map接口不同。如果在go中我们要删除map中的一个元素怎么办?使用内置的delete函数就可以,如下代码删除ages这个map中,key为michael的元素。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n94" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

delete(ages,"michael")</pre>

如果我们想遍历map中的KV值怎么办?答案是使用range风格的for循环,可比Java Map的遍历简洁多了。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n97" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

for name,age := range ages {

fmt.Println("name:",name,",age:",age)

}</pre>

range一个map,会返回两个值,第一个是key,第二个是value,这个也是go多值返回的优势,下面会讲。

函数方法

在go中,函数和方法是不一样的,我们一般称包级别的(直接可以通过包调用的)称之为函数,比如fmt.Println();把和一个类型关联起来的函数称之为方法,如下示例:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n103" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

package libimport "time"type Person struct {

age int

name string}func (p Person) GetName() string { return p.name

}func GetTime() time.Time{ return time.Now()

}</pre>

其中GetTime()可以通过lib.GetTime()直接调用,称之为函数;而GetName()则属于Person这个结构体的函数,只能声明了Person类型的实例后才可以调用,称之为方法。

不管是函数还是方法,定义是一摸一样的。而在这里,最可以讲的就是多值返回,也就是可以同时返回多个值,这就大大为我们带来了方便,比如上个遍历map的例子,直接可以获取KV,如果只能返回一个值,我们就需要调用两次方法才可以。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n108" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

func GetTime() (time.Time,error){ return time.Now(),nil}</pre>

多值返回也很简单,返回的值使用逗号隔开即可。如果要接受多值的返回,也需要以逗号分隔的变量,有几个返回值,就需要几个变量,比如这里:

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n111" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

now,err:=GetTime()</pre>

如果有个返回值,我们用不到,不想浪费一个变量接收怎么办?这时候可以使用空标志符 _
,这是java没有的。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n114" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

now,_:=GetTime()</pre>

指针

Go的指针和C中的声明定义是一样的,其作用类似于Java引用变量效果。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n118" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

var age int = 10

var p *int = &age

*p = 11

fmt.Println(age)</pre>

其中指针p指向变量age的内存地址,如果修改*p的值,那么变量age的值也同时会被修改,例子中打印出来的值为11,而不是10.

相对应java引用类型的变量,可以理解为一个HashMap类型的变量,这个变量传递给一个方法,在该方法里对HashMap修改,删除,就会影响原来的HashMap。引用变量集合类最容易理解,自己的类也可以,不过基本类型不行,基本类型不是引用类型的,他们在方法传参的时候,是拷贝的值。

结构体替代类

Go中没有类型的概念,只有结构体,这个和C是一样的。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n126" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

type Person struct {

age int

name string}</pre>

Go中的结构体是不能定义方法的,只能是变量,这点和Java不一样的,如果要访问结构体内的成员变量,通过 .
操作符即可。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n129" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

func (p Person) GetName() string { return p.name

}</pre>

这就是通过 .
操作符访问变量的方式,同时它也是一个为结构体定义方法的例子,和函数不一样的是,在 func
关键字后要执行该方法的接收者,这个方法就是属于这个接收者,例子中是Person这个结构体。

在Go中如果想像Java一样,让一个结构体继承另外一个结构体怎么办?也有办法,不过在Go中称之为组合或者嵌入。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n134" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

type Person struct {

age int

name string

Address

}type Address struct {

city string}</pre>

结构体Address被嵌入了Person中,这样Person就拥有了Address的变量和方法,就想自己的一样,这就是组合的威力。通过这种方式,我们可以把简单的对象组合成复杂的对象,并且他们之间没有强约束关系,Go倡导的是组合,而不是继承、多态。

接口

Go的接口和Java类型,不过它不需要强制实现,在Go中,如果你这个类型(基本类型,结构体等都可以)拥有了接口的所有方法,那么就默认为这个类型实现了这个接口,是隐式的,不需要和java一样,强制使用 implement
强制实现。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n140" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

type Stringer interface {

String() string}func (p Person) String() string { return "name is "+p.name+",age is "+strconv.Itoa(p.age)

}</pre>

以上实例中可以看到,Person这个结构体拥有了fmt.Stringer接口的方法,那么就说明Person实现了fmt.Stringer接口。

接口也可以像结构体一样组合嵌套,这里不再赘述。

并发

Go并发主要靠go goroutine支持,也称之为go协程或者go程,他是语言层面支持的,非常轻量级的多任务支持,也可以把他简单的理解为java语言的线程,不过是不一样的。

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go run()</pre>

这就启动一个goroutine来执行run函数,代码非常简洁,如果在java中,需要先New一个Thread,然后在重写他的run方法,然后在start才可以开始。

两个goroutine可以通过channel来通信,channel是一个特殊的类型,也是go语言级别上的支持,他类似于一个管道,可以存储信息,也可以从中读取信息。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n153" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

package mainimport "fmt"func main() {

result:=make(chan int) go func() {

sum:=0

for i:=0;i<10;i++{

sum=sum+i

}

result<-sum

}()

fmt.Print(<-result)

}</pre>

以上示例使用一个单独的goroutine求和,当得到结果时,存放在result这个chan里,然后供main goroutine读取出来。当result没有被存储值的时候,读取result是阻塞的,所以会等到结果返回,协同工作,通过chan通信。

对于并发,go还提供了一套同步机制,都在sync包里,有,有一些常用的工具函数等,和java的concurrent框架差不多。

异常机制

相比java的Exception来说,go有两种机制,不过最常用的还是error错误类型,panic只用于严重的错误。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n161" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

type error interface {

Error() string}</pre>

go内置的error类型非常简洁,只用实现Error方法即可,可以打印一些详细的错误信息,比如常见的函数多值返回,最后一个返回值经常是error,用于传递一些错误问题,这种方式要比java throw Exception的方法更优雅。

Defer代替finally

go中没有java的finally了,那么如果我们要关闭一些一些连接,文件流等怎么办呢,为此go为我们提供了defer关键字,这样就可以保证永远被执行到,也就不怕关闭不了连接了。

<pre class="md-fences md-end-block" lang="" contenteditable="false" cid="n167" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: Monaco, Consolas, "Andale Mono", "DejaVu Sans Mono", monospace; font-size: 0.9rem; white-space: pre; margin-top: 0px; margin-bottom: 20px; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(54, 59, 64); text-align: left; break-inside: avoid; display: block; position: relative !important; padding: 10px 30px; border: 1px solid; width: inherit; color: rgb(184, 191, 198); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">

f,err:=os.Open(filename)defer f.Close()

readAll(f)</pre>

统一编码风格

在编码中,我们有时为了是否空行,大括号是否独占一行等编码风格问题争论不休,到了Go这里就终止了,因为go是强制的,比如花括号不能独占一行,比如定义的变量必须使用,否则就不能编译通过。

第二种就是go fmt这个工具提供的非强制性规范,虽然不是强制的,不过也建议使用,这样整个团队的代码看着就像一个人写的。很多go代码编辑器都提供保存时自动gofmt格式的话,所以效率也非常高。

便捷的部署

go最终生成的是一个可执行文件,不管你的程序依赖多少库,都会被打包进行,生成一个可执行文件,所以相比java庞大的jar库来说,他的部署非常方便,执行运行这个可执行文件就好了。

对于Web开发,更方便,不用安装jdk,tomcat容器等等这些环境,直接一个可执行文件,就启动了。对于go这种便捷的部署方式,我觉得他更能推进docker的服务化,因为docker就是倡导一个实例一个服务,而且不用各种依赖,layer层级又没那么多,docker image也会小很多。

原文 

https://studygolang.com/articles/18928

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