Calling Class Methods
Introduced| English | Meaning |
|---|---|
| class method/klæs ˈmeθəd/ | class method |
| static method/ˈstætɪk ˈmeθəd/ | A Java method belonging to a class, callable without creating an instance and without an implicit current object. |
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
staticin 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);stores4.0inr.- 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.
Call a class method on the CLASS name, not an object: Math.sqrt(16), never m.sqrt(16). Match the argument count and types to the method's parameters, and remember to store the return value — Math.sqrt(16); on its own computes 4.0 and then throws it away. Empty parentheses are still required when there are no arguments.
Combining class method calls:
int bigger = Math.max(3, 8);→biggeris8.double root = Math.sqrt(bigger + 1);→Math.sqrt(9)→3.0.- A return value (
8) fed straight into the next call.
A class (static) method is called on the class name: Math.sqrt(16). Pass the right arguments (matched by position and type) in parentheses, and store the return value in a variable to use it. This differs from an instance method, which is called on an object.
Calling a static method
Math.max is called on the class and returns the larger value.
How do you correctly call the static method sqrt from the Math class?
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Class methods are called on the class name with a dot.
What does Math.max(3, 8) return?
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max returns the larger of the two arguments.
The keyword that marks a method as a class (static) method is...
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static means the method belongs to the class, not an object.
Math.sqrt(16); on its own line stores 4.0 for later use.
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It computes 4.0 but discards it — you must store the return value.
A class method is called on the class name, while an instance method is called on an object.
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Math.abs(-5) (class) vs word.length() (object).