[groovy] closure closure (customize closure parameters | customize a single closure parameter | customize multiple closure parameters | specify the default value of closure parameters)

One 、 Custom closure parameter list

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If you want to Closure in , Passing multiple parameters , need by Closure Specify the parameter list ;

Specify a parameter list for the closure , Need to be in closure The starting position uses " -> " Symbol , Specify the parameter list on the left side of the symbol ;

1、 Define the closure of a custom parameter

stay " -> " Write a variable to the left of the symbol a , here The variable a Can receive any type of value , This parameter can be printed in the closure a Value ;

        //  Define closure variables  ,  Declare a parameter  a        def closure3 = { 
     a ->            println "${a}"        }        //  Call closure  ,  Cannot pass in parameters         closure3.call(1);        closure3(2);

The print result of the above closure is :

12

2、 Define closures for multiple custom parameters

stay " -> " Write multiple variables to the left of the symbol , Variables are separated by commas , Such as a , b , At this point, the closure can receive multiple parameters , These two parameters can be of any type ;

        //  Define closure variables  ,  Declare two parameters  a, b        //  Print these two parameters in the closure         def closure4 = { 
     a, b ->            println "${a} : ${b}"        }        //  Call closure  ,  Cannot pass in parameters         closure4.call(1, 2);        closure4(3, 4);

The result is :

1 : 23 : 4

3、 Specify default values for closure parameters

In closure , have access to Parameter name = The default value is The way , After specifying the default value for the closure parameter , When a closure is called , You can not pass in this parameter with default value ;

If Closure Parameters All have default values ,

• Sure No parameters are passed ;
• If you pass $1$

If Closure Parameters , Some have default values , Some have no default values , Suppose there is

2

2

2 Parameters , Yes

1

1

1 Each has a default value ,

1

1

1 There is no default value ;

• If Pass on

  2

  2

  2 Parameters , Then assign values from left to right ;

• If you deliver $1$

Code example :

        // V.  Specify default values for closure parameters         //  Define closure variables  ,  Declare two parameters  a, b        //  And specify the default value for the closure         def closure5 = { 
     a = 0, b = "Groovy" ->            println "${a} : ${b}"        }        //  Closures have default values  ,  You can call without passing in parameters         closure5()

Execution results :

0 : Groovy

Two 、 Complete code example

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Complete code example :

import org.codehaus.groovy.ant.Groovyclass Test { 
        static void main(args) { 
            // III.  Receive a closure of a custom parameter         //  Define closure variables  ,  Declare a parameter  a        def closure3 = { 
     a ->            println "${a}"        }        //  Call closure  ,  Cannot pass in parameters         closure3.call(1);        closure3(2);        // IV.  Receive the closure of two custom parameters         //  Define closure variables  ,  Declare two parameters  a, b        //  Print these two parameters in the closure         def closure4 = { 
     a, b ->            println "${a} : ${b}"        }        //  Call closure  ,  Cannot pass in parameters         closure4.call(1, 2);        closure4(3, 4);        // V.  Specify default values for closure parameters         //  Define closure variables  ,  Declare two parameters  a, b        //  And specify the default value for the closure         def closure5 = { 
     a = 0, b = "Groovy" ->            println "${a} : ${b}"        }        //  Closures have default values  ,  You can call without passing in parameters         closure5()    }}

Execution results :

121 : 23 : 40 : Groovy