a quick tutorial on lambda expressions

Quick Intro to Lambda Expressions in Java 8

Parth Joshi

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Anonymous Inner class

• Reprise:

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Anonymous Inner class• Reprise:



Anonymous Inner class• Reprise:

Anonymous Inner Class

Anonymous Inner Class




• Issue:

• If the implementation of your anonymous class is very simple, such as an interface that contains only one method, then the syntax of anonymous classes may seem unwieldy and unclear.

• In these cases, you're usually trying to pass functionality as an argument to another method, such as what action should be taken when someone clicks a button.




• Solution in Java 8:

• Lambda expressions enable you to do this,

1. to treat functionality as method argument,

2. or code as data.



Lambda Expression

• Conventional Anonymous class



Lambda Expression

• Conventional Anonymous class

Lambda Expression



Lambda Expression

• Important notes:

• You need to use this with functional interface only. Anonymous inner classes with abstract class instantiation will not work here.



Lambda Expression

• Important notes:

• We cannot use multiple function declarations in the interface. There will be ambiguity in lambda expressions in that case:

Compile Time Error: incompatible types: PrintMessage is not a functional interfacemultiple non-overriding abstract methods found in interface PrintMessage



Lambda Expression Characteristics

Optional Type Declaration

Optional parenthesis around parameter

Optional curly braces

Optional return value








Consider the following declarations:

interface PrintMessage {

public void print(String message);

// public void print2(String message 2)

}

interface SimpleMaths {

public int arithmatic(int a, int b);

}












}



}

We can pass arguments without type declarations

//with type declaration

SimpleMaths addition = (int a, int b) -> {return a + b;};

//without type declaration

SimpleMaths subtraction = (a, b) -> {return a - b;};










}



}

For a single argument in the functional interface, () are not required

// message with parenthesis

PrintMessage helloMessage =

(String message) -> {System.out.println("Hello world");};

// optional paranthesis around parameter.

// this only works with single argumnent

PrintMessage sayHi = message-> {System.out.println("Hi");};










}



}

No need to use {} in case of single statement expression

PrintMessage sayHi = message-> System.out.println("Hi");










}



}

In case of single expression, compiler returns the value of expression

// single statement, returns the value of expression.

SimpleMaths multiplication = (a , b) -> a*b;



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a quick tutorial on lambda expressions

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