Method Reference :: Operator illustrated

I have not seen any atomic & accessible illustrations of the use of method reference operator (::) in Java.

The method reference operator (::) is a shorthand which tells the Java JVM to pass parameters automatically to a method. 

If your lambda expression is like this:

str -> System.out.println(str)

then you can replace it with a method reference like this:

System.out::println

The above is a simple example with simpler & easier examples and instances to follow

The way the following illustrations work is so: first we will illustrate the straightforward way of doing it and then we will illustrate the same thing using the reference method operator (::).

Method reference to a static method of a class

Following illustrates passing parameters to a static method:

[BEGIN CODE] [/END CODE]

The print out from the above code is:

 

Line 8 above goes over the straightforward implementation of taking an arraylist & going over its elements and printing them out. Line 8 says : take an element of the messages arraylist as the str variable (short for string) and print out the string variable str. Then Line 9 does the same thing as line 8 but using the method reference (::) operator. All the rest of the examples will follow the same pattern. 

Method reference to an instance method of an object

The source code would be:

[BEGIN CODE] [/BEGIN CODE]

The output from the above source code would be:

As you may observe from above (line 19) illustrates the use of the instance method of a String object (alpha) , the instance method being startsWith. Line 19 illustrates the straightforward implementation (without using the method reference operator ::) . In contast Line 23 illustrates the use of the method reference operator (::).

Method reference to an instance method of an instance to be determined at runtime

The source code would be:

[BEGIN CODE] [/BEGIN CODE]

The out put from the source code above would be:

As you may observe from above (line 17) illustrates the use of the instance method of a String object (txt) , the instance method being isEmpty. Although Line 17 illustrates the use of a straighforward lambda expression line 19 illustrates the employment of the refrence method operator (::).

Method reference to the constructor of a Class

The source code would be:

[BEGIN CODE] [/BEGIN CODE]

The out put from the source code above would be:

As you may observe from above (line 7) illustrates the use of the constructor of an Example object . Although Line 7 illustrates the use of a straighforward lambda expression line 8 illustrates the employment of the refrence method operator (::).