Chapter 28: Methods in Java

This chapter is only about the idea of a method and how to declare and call simple ones—including void methods that return nothing. Parameters get extra depth in Chapter 29; return types beyond “preview” are Chapter 30; overloading is Chapter 31.

1. Topic title

Methods: named blocks you call to avoid copy-paste and to name intent

2. What it means

A method is a named sequence of statements with optional inputs (parameters) and optional output (return value). You declare it once inside a class, then invoke it many times.

static void greet(String name) {
    System.out.println("Hello, " + name);
}

• static here means “belongs to the class, not a specific object instance.” You can call it from main without new—handy for learning. Object instance methods come with OOP chapters later.
• void means the method does not send a value back to the caller—it might print, mutate something passed in, etc.
• greet is the method name.
• (String name) is the parameter list (Chapter 29 zooms in).

3. Why it is used

DRY — Don’t Repeat Yourself. If you print the same banner in five places, one printBanner() method updates behavior everywhere.

Readability — computeTotalWithTax(...) reads better than twenty lines of math inline.

Testing — later you can call small methods from unit tests (Chapter 146 area).

4. Real-world example

A CLI tool might parse arguments in main, then call runHelp(), runMigrate(), runReport() based on a verb. Each verb is a method—easy to navigate in the IDE.

5. Java code example

public class MethodsIntroDemo {
 
    static void line() {
        System.out.println("--------------------");
    }
 
    static void greetTwice(String who) {
        greetOnce(who);
        greetOnce(who);
    }
 
    static void greetOnce(String who) {
        System.out.println("Hi " + who);
    }
 
    static void showSum(int a, int b) {
        System.out.println(a + b);
    }
 
    public static void main(String[] args) {
        line();
        greetTwice("Sam");
        line();
        showSum(2, 3);
    }
}

Output:

--------------------
Hi Sam
Hi Sam
--------------------
5

6. Explanation of code

• line takes no parameters, returns nothing—pure side effect (printing).
• greetTwice calls greetOnce twice—methods calling methods is normal.
• showSum demonstrates two int parameters (details in Chapter 29).
• main stays short: orchestration only.

7. Common mistakes

Declaring a method inside another method — not allowed in Java; methods live at class level.

Forgetting static when calling from static main without an object—beginners hit “cannot be referenced from a static context.”

Missing return type — every method needs a type or void.

Wrong method name casing — Java is case-sensitive; Greet ≠ greet.

8. Best practices

Verb names for methods that do actions: save, calculate, print.

Keep main thin — parse args, call a few methods, done.

One clear purpose per method — if the name needs “and,” split.

9. Small practice task

Add a method static void printBox(String title) that prints a line of =, then the title, then another line of =. Call it twice from main with different titles.

Beginner tip

Use Jump to definition in the IDE on greetTwice → greetOnce until navigation feels natural. That is how professionals read unfamiliar codebases.