"Go for Java Programmers" Go programming for Java Developers 2

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Conditional statements

Go does not use parentheses in conditional statements, such as conditional statements, expressions for conditional statements if for , switch or values of conditional statements. On the other hand, it does not need to if for add curly braces in or conditional statements

If a < b {f ()}if (A < b) {f ()}           //brackets are unnecessary. If (a < b) f ()               //invalid for i = 0; I < i++ {}for (i = 0) ; I < 10; i++) {}  //invalid

In addition, if and switch receive an optional initialization state, then the usual practice is to build a local variable

If err: = file. Chmod (0664); Err! = Nil {    log. Print (ERR)    return err}

For statement

Go does not have a statement while do-while . When for the condition of a statement is relatively single, his function is like a while statement. Completely omitting the condition produces a dead loop.

forStatements may contain range traversal strings, arrays, slices, maps, or channels. Except as written below.

For I: = 0; I < Len (a); i++ {...}

athe elements to be traversed can also be written as

For I, V: = Range A {...}

This refers to the i index, which v represents the contiguous element of array, slice, or string. For a string, I is the index of a byte, v pointing to rune rune int32 an alias of type (type). The maps iteration produces a key-value pair, and channels produces only one iteration value.

Break and Continue

Like Java, go permits break and continue to specify a label, but the label must refer to for , switch or select statement.

Switch statement

In the switch statements, the case tags do not pass by default, but you can get them to fallthrough end the statement by passing the case.

Switch N {case 0:  //Empty case Bodycase 1:    f ()  //F was not called when n = = 0.}

But one case can contain over a value

Switch N {case 0, 1:    f ()  //F is called if n = = 0 | | n = = 1.}

caseValues can support any type of equality comparison operator, such as a string or pointer. A switch statement that loses an expression is equivalent to the expression true .

switch {case N < 0:    F1 () case n = = 0:    f2 () Default:    F3 ()}

+ + and--statements

++And -- can only be used as postfix operators, and only in statements, not in expressions. For example, you may not write n = i++ .

Defer statements

deferThe execution of the statement call to a function is deferred until the function returns that moment. deferwhen the statement executes, the parameters of the deferred function are computed and saved for future use

F, err: = OS. Open ("filename") defer f.close ()  //F'll is closed when the This function returns.

Constants (constant)

The constants in go may be untyped . This applies to numeric literals of untyped constant expressions, and to const non-type constant expressions that use declarations. When it is used in a context that requires a value of a band type, an untyped constant can be converted into a typed value. The use of this constant is relatively free, even if go does not have an implicit type conversion

var a uintf (A + 1)    //The untyped numeric constant 1 becomes typed as uint.f (A + 1e3)  //1E3 is also typed as uint .

The language has no limit on the size of untyped numeric constants. Restrictions apply only when a constant is used, and one of these types is required.

Const HUGE = 1 << 100var n int = huge >> 98

If the type of a variable declaration is not present and the corresponding expression evaluates to an untyped numeric constant, the constant is converted to rune ,, int float64 , or complex128 type, depending on whether the value is a character, integer, floating point, or complex constant.

c: = ' rune '      //(alias for Int32) N: = 1 + 2    //INTX: = 2.7      //float64z: = 1 + 2i   //complex128

GO does not exist with enum type. Instead, you can use a special name iota in a single const declaration to get a series of accumulated values. When the initialization expression is omitted as one const , it reuses the preceding expression.

Const (    red = Iota  //Red = = 0    blue        //blue = 1    green       //green = = 2)

Structs (structural body)

structs correspond to classes in Java, but members of a struct cannot be methods, but variables. The pointer to the struct is a Java-like reference variable. Unlike Java classes, structs can also be defined as direct values. In both cases . , use to access the members of the struct.

Type mystruct struct {    s string    n int64}var x mystruct      //x is initialized to mystruct{"", 0}.var px *mystruct    //PX is initialized to nil.px = new (MyStruct)  //PX points to the new struct mystruct{"", 0}.x.s = "Foo" PX.S = "Bar"

In Go, a method can be associated with any named type, not just with a struct. See the discussion of methods and interfaces for details.

Pointers (pointer)

If you have an int or struct or an array that needs to be assigned the content copy of the object. To achieve the effect of a reference variable in Java, Go uses pointers. For any type E T , there is a corresponding pointer type that *T represents T the value of the pointer type

Assign storage space to pointer variables, use built-in functions new , pass in a type, and return a pointer to the allocated storage space. The allocated space will be initialized by 0 type. For example, the new(int) assignment is stored as a new int, initializes its value to E 0 , and returns its address, type *int .

Java code T p = new T() , which T is a two int -type instance variable a and a b class that corresponds to the

Type T struct {A, B int}var p *t = new (t)

Or do it habitually.

P: = new (T)

var v TRepresents a declaration that declares that a variable contains a value type T , which is not in Java. You can also create and initialize values using a composite method.

V: = t{1, 2}

Equivalent to

var v tv.a = 1V.B = 2

For operands of type T x , the address operator &x provides the address of the value type *T x ,

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2012-12-17