[JAVA] How to create a method

What is a method? A process that has been named so that it can be called at any time. For example, when I wanted to write "Hello World" 10 times ...


System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");
System.out.println("Hello World");

It is troublesome to write. If you use the method, you can write as follows.


void sayHelloWorld(int n){
  for(int i=1; i<=n; i++){
  System.out.println("Hello World");

Once you have created a method for that process, you can call it at any time.

How to create a method Basically, it's almost the same as when creating variables. There is a part that describes the argument and a part that describes the process. In the above example, (1) "void" specifies the type of the result to be displayed. (2) "sayHelloWorld" determines the name of the method (the name used when calling). ③ You can specify an argument with "(int n)". (If not specified, only "()" is written after the method name.) (4) Specify the process to be executed by the code inside "{}". ⑤ In "say Hello World (10)", the process created above is executed 10 times.

Return value In the case of the method introduced above, the processing is only character input. If you set it as a return value when you output the result in the contents of the method, you can use it when you connect the result of the process of that method to another process.

Of course, even if the type name is "void", it is possible to get the result calculated by "System.out.println ();". The return value is effective when you want to obtain the result of processing as "moving decimal point, integer value, boolean value" instead of "character string".

For example Suppose you want to get the automatically calculated result by entering the list price of a certain product and the discount rate (% off) of that product.


double calculationOfDiscountPrice(int price, double discountRate){
  double discountPrice = price - (price*discountRate/100);
  return discountPrice

↓ 900

You can get the result like this.

Parameters In addition, it is described in the first line of "method2.jv". 「double calculationOfDiscountPrice(int price, double discountRate)」 The part inside () is called a parameter, and multiple settings can be made. (Variables that can be given in the method) 「calculationOfDiscountPrice(1000,10)」 The (1000,10) part of is called an "argument" and is a numerical value / character string to be included in the parameter.

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