Which of the following method calls illustrates the return value of a method as a parameter?

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Func Delegate
In this article
Extension Methods
When calling a method a value sent to the method is called?
What are method parameters in Java?
How do you call a method using parameters?
What is the keyword used to pass a value back to the calling method?

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Function without return type stands for a void function. The void function may take multiple or zero parameters and returns nothing. Here, we are going to define a method which takes 2 parameters and doesn’t return anything.

Syntax:

public static void function(int a, int b)

Example:

public static void fun1(String 1, String 2){ // method execution code };

Approach:

Take 2 inputs into two variables.
Pass these inputs as an argument to the function.
Display the sum from this defined function.

Code:

Java

import java.util.*;

public class Main {

public static void main(String args[])

{

int a = 4;

int b = 5;

calc(a, b);

}

public static void calc(int x, int y)

{

int sum = x + y;

System.out.print("Sum of two numbers is :" + sum);

}

Output

Sum of two numbers is :9

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Func Delegate

Reference

Definition

Encapsulates a method that has no parameters and returns a value of the type specified by the TResult parameter.

Examples

The following example demonstrates how to use a delegate that takes no parameters. This code creates a generic class named LazyValue that has a field of type Func. This delegate field can store a reference to any function that returns a value of the type that corresponds to the type parameter of the LazyValue object. The LazyValue type also has a Value property that executes the function (if it has not already been executed) and returns the resulting value.

The example creates two methods and instantiates two LazyValue objects with lambda expressions that call these methods. The lambda expressions do not take parameters because they just need to call a method. As the output shows, the two methods are executed only when the value of each LazyValue object is retrieved.

using System; static class Func1 { public static void Main() { // Note that each lambda expression has no parameters. LazyValue lazyOne = new LazyValue(() => ExpensiveOne()); LazyValue lazyTwo = new LazyValue(() => ExpensiveTwo("apple")); Console.WriteLine("LazyValue objects have been created."); // Get the values of the LazyValue objects. Console.WriteLine(lazyOne.Value); Console.WriteLine(lazyTwo.Value); } static int ExpensiveOne() { Console.WriteLine("\nExpensiveOne() is executing."); return 1; } static long ExpensiveTwo(string input) { Console.WriteLine("\nExpensiveTwo() is executing."); return (long)input.Length; } } class LazyValue where T : struct { private Nullable val; private Func getValue; // Constructor. public LazyValue(Func func) { val = null; getValue = func; } public T Value { get { if (val == null) // Execute the delegate. val = getValue(); return (T)val; } } } /* The example produces the following output: LazyValue objects have been created. ExpensiveOne() is executing. 1 ExpensiveTwo() is executing. 5 */ open System type LazyValue<'T>(func: Func<'T>) = let mutable value = ValueNone member _.Value = match value with | ValueSome v -> v | ValueNone -> // Execute the delegate. let v = func.Invoke() value <- ValueSome v v let expensiveOne () = printfn "\nExpensiveOne() is executing." 1 let expensiveTwo (input: string) = printfn "\nExpensiveTwo() is executing." int64 input.Length // Note that each lambda expression has no parameters. let lazyOne = LazyValue(fun () -> expensiveOne ()) let lazyTwo = LazyValue(fun () -> expensiveTwo "apple") printfn "LazyValue objects have been created." // Get the values of the LazyValue objects. printfn $"{lazyOne.Value}" printfn $"{lazyTwo.Value}" // The example produces the following output: // LazyValue objects have been created. // // ExpensiveOne() is executing. // 1 // // ExpensiveTwo() is executing. // 5 Public Module Func Public Sub Main() ' Note that each lambda expression has no parameters. Dim lazyOne As New LazyValue(Of Integer)(Function() ExpensiveOne()) Dim lazyTwo As New LazyValue(Of Long)(Function() ExpensiveTwo("apple")) Console.WriteLine("LazyValue objects have been created.") ' Get the values of the LazyValue objects. Console.WriteLine(lazyOne.Value) Console.WriteLine(lazyTwo.Value) End Sub Public Function ExpensiveOne() As Integer Console.WriteLine() Console.WriteLine("ExpensiveOne() is executing.") Return 1 End Function Public Function ExpensiveTwo(input As String) As Long Console.WriteLine() Console.WriteLine("ExpensiveTwo() is executing.") Return input.Length End Function End Module Public Class LazyValue(Of T As Structure) Private val As Nullable(Of T) Private getValue As Func(Of T) ' Constructor. Public Sub New(func As Func(Of T)) Me.val = Nothing Me.getValue = func End Sub Public ReadOnly Property Value() As T Get If Me.val Is Nothing Then ' Execute the delegate. Me.val = Me.getValue() End If Return CType(val, T) End Get End Property End Class

Remarks

You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have no parameters and must return a value.

Note

To reference a method that has no parameters and returns void (unit, in F#) (or in Visual Basic, that is declared as a Sub rather than as a Function), use the Action delegate instead.

When you use the Func delegate, you do not have to explicitly define a delegate that encapsulates a parameterless method. For example, the following code explicitly declares a delegate named WriteMethod and assigns a reference to the OutputTarget.SendToFile instance method to its delegate instance.

using System; using System.IO; delegate bool WriteMethod(); public class TestDelegate { public static void Main() { OutputTarget output = new OutputTarget(); WriteMethod methodCall = output.SendToFile; if (methodCall()) Console.WriteLine("Success!"); else Console.WriteLine("File write operation failed."); } } public class OutputTarget { public bool SendToFile() { try { string fn = Path.GetTempFileName(); StreamWriter sw = new StreamWriter(fn); sw.WriteLine("Hello, World!"); sw.Close(); return true; } catch { return false; } } } open System.IO type WriteMethod = delegate of unit -> bool type OutputTarget() = member _.SendToFile() = try let fn = Path.GetTempFileName() use sw = new StreamWriter(fn) sw.WriteLine "Hello, World!" true with _ -> false let output = new OutputTarget() let methodCall = WriteMethod output.SendToFile if methodCall.Invoke() then printfn "Success!" else printfn "File write operation failed." Imports System.IO Delegate Function WriteMethod As Boolean Module TestDelegate Public Sub Main() Dim output As New OutputTarget() Dim methodCall As WriteMethod = AddressOf output.SendToFile If methodCall() Then Console.WriteLine("Success!") Else Console.WriteLine("File write operation failed.") End If End Sub End Module Public Class OutputTarget Public Function SendToFile() As Boolean Try Dim fn As String = Path.GetTempFileName Dim sw As StreamWriter = New StreamWriter(fn) sw.WriteLine("Hello, World!") sw.Close Return True Catch Return False End Try End Function End Class

The following example simplifies this code by instantiating the Func delegate instead of explicitly defining a new delegate and assigning a named method to it.

using System; using System.IO; public class TestDelegate { public static void Main() { OutputTarget output = new OutputTarget(); Func methodCall = output.SendToFile; if (methodCall()) Console.WriteLine("Success!"); else Console.WriteLine("File write operation failed."); } } public class OutputTarget { public bool SendToFile() { try { string fn = Path.GetTempFileName(); StreamWriter sw = new StreamWriter(fn); sw.WriteLine("Hello, World!"); sw.Close(); return true; } catch { return false; } } } open System open System.IO type OutputTarget() = member _.SendToFile() = try let fn = Path.GetTempFileName() use sw = new StreamWriter(fn) sw.WriteLine "Hello, World!" true with _ -> false let output = OutputTarget() let methodCall = Func output.SendToFile if methodCall.Invoke() then printfn "Success!" else printfn "File write operation failed." Imports System.IO Module TestDelegate Public Sub Main() Dim output As New OutputTarget() Dim methodCall As Func(Of Boolean) = AddressOf output.SendToFile If methodCall() Then Console.WriteLine("Success!") Else Console.WriteLine("File write operation failed.") End If End Sub End Module Public Class OutputTarget Public Function SendToFile() As Boolean Try Dim fn As String = Path.GetTempFileName Dim sw As StreamWriter = New StreamWriter(fn) sw.WriteLine("Hello, World!") sw.Close Return True Catch Return False End Try End Function End Class

You can use the Func delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods.)

using System; using System.IO; public class Anonymous { public static void Main() { OutputTarget output = new OutputTarget(); Func methodCall = delegate() { return output.SendToFile(); }; if (methodCall()) Console.WriteLine("Success!"); else Console.WriteLine("File write operation failed."); } } public class OutputTarget { public bool SendToFile() { try { string fn = Path.GetTempFileName(); StreamWriter sw = new StreamWriter(fn); sw.WriteLine("Hello, World!"); sw.Close(); return true; } catch { return false; } } }

You can also assign a lambda expression to a Func delegate, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (VB), Lambda Expressions (C#), and Lambda Expressions (F#).)

using System; using System.IO; public class Anonymous { public static void Main() { OutputTarget output = new OutputTarget(); Func methodCall = () => output.SendToFile(); if (methodCall()) Console.WriteLine("Success!"); else Console.WriteLine("File write operation failed."); } } public class OutputTarget { public bool SendToFile() { try { string fn = Path.GetTempFileName(); StreamWriter sw = new StreamWriter(fn); sw.WriteLine("Hello, World!"); sw.Close(); return true; } catch { return false; } } } open System open System.IO type OutputTarget() = member _.SendToFile() = try let fn = Path.GetTempFileName() use sw = new StreamWriter(fn) sw.WriteLine "Hello, World!" true with _ -> false let output = OutputTarget() let methodCall = Func(fun () -> output.SendToFile()) if methodCall.Invoke() then printfn "Success!" else printfn "File write operation failed." Imports System.IO Module TestDelegate Public Sub Main() Dim output As New OutputTarget() Dim methodCall As Func(Of Boolean) = Function() output.SendToFile() If methodCall() Then Console.WriteLine("Success!") Else Console.WriteLine("File write operation failed.") End If End Sub End Module Public Class OutputTarget Public Function SendToFile() As Boolean Try Dim fn As String = Path.GetTempFileName Dim sw As StreamWriter = New StreamWriter(fn) sw.WriteLine("Hello, World!") sw.Close Return True Catch Return False End Try End Function End Class

The underlying type of a lambda expression is one of the generic Func delegates. This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. In particular, because many methods of types in the System.Linq namespace have Func parameters, you can pass these methods a lambda expression without explicitly instantiating a Func delegate.

If you have an expensive computation that you want to execute only if the result is actually needed, you can assign the expensive function to a Func delegate. The execution of the function can then be delayed until a property that accesses the value is used in an expression. The example in the next section demonstrates how to do this.

Which of the following method calls illustrates the return value of a method as a parameter?

Java

Func Delegate

Definition

In this article

Type Parameters

Return Value

Examples

Remarks

Extension Methods

Applies to

See also

When calling a method a value sent to the method is called?

What are method parameters in Java?

How do you call a method using parameters?

What is the keyword used to pass a value back to the calling method?

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