استدعاء طرق الفئة

Calling a class method

• A class method 类方法 (a static method 静态方法) belongs to the class itself, not to an object.
• Call it with the class name and a dot: Math.sqrt(16), Integer.parseInt("42").
• No object needs to exist — the method lives on the class.
• The keyword static in the header marks a method as a class method.

Passing arguments

• Put the arguments inside the parentheses: Math.max(3, 8).
• The values are matched to the method's parameters, by position.
• Give the right number and types of arguments, or it won't compile.
• No arguments? Still write the empty parentheses: sc.nextLine().

A class method is called on the class name: Math.sqrt(25.0)

Using the return value

• Most class methods return a value — capture it in a variable.
• double r = Math.sqrt(16); stores 4.0 in r.
• Ignoring a useful return value usually means you forgot to store the result.
• A returned value can also feed straight into another expression.

Static vs. instance — a first look

• A class (static) method is called on the class: Math.abs(-5).
• An instance method (next lessons) is called on an object: word.length().
• The tell: is there a dot after a class name or after an object?
• Class methods don't need an object; instance methods do.