Gopher面试中的Coding（二）

08-31 Mark 395

##1.写出下面代码输出内容：

```go
package main

import (
		"fmt"
)

func main() {
		defer_call()
}

func defer_call() {
		defer func() { fmt.Println("打印前") }()
		defer func() { fmt.Println("打印中") }()
		defer func() { fmt.Println("打印后") }()

panic("触发异常")
}
```
输出结果：
```
打印后
打印中
打印前
panic: 触发异常
```
问题原因：
- defer的执行顺序是逆序的，也就是先进后出的顺序；
- panic在函数最终执行完毕才抛出异常；

##2.这段代码能编译通过吗？

```go
package main

import (
		"fmt"
)

type People interface {
		Speak(string) string
}

type Stduent struct{}

func (stu *Stduent) Speak(think string) (talk string) {
		if think == "bitch" {
				talk = "You are a good boy"
		} else {
				talk = "hi"
		}
		return
}

func main() {
		var peo People = Stduent{}
		think := "bitch"
		fmt.Println(peo.Speak(think))
}
```
输出结果：
```
# command-line-arguments
.\defer.go:23: cannot use Stduent literal (type Stduent) as type People in assignment:
        Stduent does not implement People (Speak method has pointer receiver)
```

问题原因：
接口赋值使用值作为参数传递var peo People = Stduent{}或者var peo People = &Stduent{}；如果使用指针作为参数传递,则只能使用var peo People = &Stduent{}

##3、下面这段代码输出的值为：
```golang
func main(){
		jsonStr := []byte(`{"age":1}`)
		var value map[string]interface{}
		json.Unmarshal(jsonStr,&value)
		age := value["age"]
		fmt.Println(reflect.TypeOf(age))
}
```
输出结果：
```golang
float64
```

问题原因：
To unmarshal JSON into an interface value, Unmarshal stores one of these in the interface value:
- bool, for JSON booleans
- float64, for JSON numbers
- string, for JSON strings
- []interface{}, for JSON arrays
- map[string]interface{}, for JSON objects
- nil for JSON null

Json数据类型中没有整数，所有的数字类型在json中都存储为float64类型。