Introduction to Go for Java Programmers
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This document provides examples of Go language concepts like variables, functions, methods, structs, interfaces, concurrency, error handling and more. It demonstrates variable declaration, multiple return values, named return parameters, arrays, slices, maps, structs with methods, interfaces, embedding interfaces, goroutines, channels, recovery from panics, and passing values vs references.
![package main
import "fmt"
func main() {
arr1 := [3] int{1, 2, 3}
arr2 := arr1
fmt.Println("arr1 is equal to arr2: ", arr1 == arr2) // true
arr3 := [4] int{1, 2, 3, 4}
fmt.Println("arr1 is equal to arr3: ", arr1 == arr3) // this is an invalid operation
}
Arrays copying and array comparison](https://image.slidesharecdn.com/introductiontogoforjavaprogrammers-151023194443-lva1-app6892/85/Introduction-to-Go-for-Java-Programmers-14-320.jpg)
![package main
import "fmt"
func PrintSlice(slice []string) {
for index, value := range (slice) {
fmt.Println(index, " : ", value)
}
}
func main() {
slice := []string{"A", "B", "C"}
PrintSlice(slice)
fmt.Println("Second element of the slice : ", slice[1:2])
slice = append(slice, "D", "E", "F")
PrintSlice(slice)
}
๏
Slice append and range keyword](https://image.slidesharecdn.com/introductiontogoforjavaprogrammers-151023194443-lva1-app6892/85/Introduction-to-Go-for-Java-Programmers-15-320.jpg)
![๏
package main
import "fmt"
func printMap(timeZone map[string]int) {
for code, timeDiff := range (timeZone) {
fmt.Println(code, " : ", timeDiff)
}
}
func main() {
var timeZone = map[string]int{
"UTC": 0 * 60 * 60,
"EST": -5 * 60 * 60,
}
// check whether a key is in the Map
_, present := timeZone["IST"]
fmt.Println("Availability of IST timezone: ", present)
printMap(timeZone)
}
Timezone sample in Maps](https://image.slidesharecdn.com/introductiontogoforjavaprogrammers-151023194443-lva1-app6892/85/Introduction-to-Go-for-Java-Programmers-16-320.jpg)
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Introduction to Go for Java Programmers
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- 3. ๏ ๏ ๏ ๏ ๏
- 8. ๏ var x int ๏ var x int = 10 ๏ var x = 10 ๏ x := 10 // only inside a function
- 9. ๏ ๏ ๏ ๏
- 10. ๏ ๏ ๏ ๏ defer
- 11. package functions import "os" func processFile(fileName string) (result string, characterCount int) { file, err := os.Open(fileName) if err != nil { // handle error } // do some file processing defer file.Close() content := "Sample content" count := len(result) return content, count } Multiple return values and defer keyword
- 12. package functions import "os" func processFile(fileName string) (result string, characterCount int) { file, err := os.Open(fileName) if err != nil { // handle error } // do some file processing defer file.Close() result = "Sample content" characterCount = len(result) return } Named return parameters
- 13. ๏ ๏ ๏ ๏
- 14. package main import "fmt" func main() { arr1 := [3] int{1, 2, 3} arr2 := arr1 fmt.Println("arr1 is equal to arr2: ", arr1 == arr2) // true arr3 := [4] int{1, 2, 3, 4} fmt.Println("arr1 is equal to arr3: ", arr1 == arr3) // this is an invalid operation } Arrays copying and array comparison
- 15. package main import "fmt" func PrintSlice(slice []string) { for index, value := range (slice) { fmt.Println(index, " : ", value) } } func main() { slice := []string{"A", "B", "C"} PrintSlice(slice) fmt.Println("Second element of the slice : ", slice[1:2]) slice = append(slice, "D", "E", "F") PrintSlice(slice) } ๏ Slice append and range keyword
- 16. ๏ package main import "fmt" func printMap(timeZone map[string]int) { for code, timeDiff := range (timeZone) { fmt.Println(code, " : ", timeDiff) } } func main() { var timeZone = map[string]int{ "UTC": 0 * 60 * 60, "EST": -5 * 60 * 60, } // check whether a key is in the Map _, present := timeZone["IST"] fmt.Println("Availability of IST timezone: ", present) printMap(timeZone) } Timezone sample in Maps
- 17. ๏ type Point struct { x, y float64 } ๏ point1 := Point{12.57777, 3.75} point2 := Point{x:10}
- 18. package main import "fmt" type Point struct { x, y int } func (point Point) toString() { fmt.Println("X: ", point.x, ", Y: ", point.y) } func (point Point) scale(scale int) { point.x *= scale; point.y *= scale } func (point *Point) scale2(scale int) { point.x *= scale; point.y *= scale } Structures, methods - and passing by-value and passing by-reference
- 19. ๏ ๏ ๏
- 20. package main import "math" type Cup struct { color string radius, length float64 sellingPrice float64 } type SellingItem interface { price() float64 } func (cup Cup) price() float64 { return cup.sellingPrice * 0.95 } Interfaces
- 21. type Shape interface { volume() float64 } func (cup Cup) volume() float64 { return math.Pi * math.Pow(cup.radius, 2) * cup.length } … Implementing a new interface ๏
- 22. ๏ ๏ ๏ ๏
- 24. package main func doSomething(channel chan int) { // do something here channel <- 1 } func main() { channel := make(chan int) go doSomething(channel) // wait until doSomething() is completed <-channel // continue with the execution of main() } Wait until a goroutine is completed
- 25. ๏ ๏ ๏
- 26. package main import "os" type Reader interface { Read(f os.File) error } type Writer interface { Write(f os.File) error } type ReadWriter interface { Reader Writer } Embedding interfaces within an interface
- 27. ๏ ๏ ๏ ๏
- 28. package main import ( "fmt" ) func B() { panic("Panic in function B") } func A() { defer func() { err := recover() fmt.Println(err) }() B() } func main() { A() } Using recovery keyword in error handling
- 29. ๏ ๏ ๏ ๏ ๏
- 30. ๏ ๏ ๏