Organize behavior with methods and objects
Define a reusable method and model data with a simple class.
- Call a method on an object and use its returned value.
A method gives a name to a reusable operation. A method can accept parameters and return a value. A class describes a kind of object with fields and methods; an object is a particular instance created from that class. This lets related state and behavior live together.
1class Rectangle {
2 int width;
3 int height;
4
5 int area() {
6 return width * height;
7 }
8}area() returns width × height
A constructor can initialize fields when a new object is created. this.width refers to the current object’s width field. Java’s standard library also provides classes for common data structures and tasks; choose a simple class design that makes each responsibility clear.
Key takeaways
Call a method on an object and use its returned value.
Java checks types as it compiles your source.
Use compiler messages as clues about what needs fixing.
Lesson quiz
4 questions · pass with 3 correct · up to 50 XP
Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.
Practice: write Java
Write Java in the editor and run it against sample input with a remote compiler. Your code is sent to Compiler Explorer to compile and run.
Calculate a rectangle’s area
Complete the Rectangle class with a constructor and area() method. Read width and height, create a Rectangle, and print its area.
- Three by four
- Five by two
Java is compiled and run by Compiler Explorer (godbolt.org), a free public service. Your source code and test input are sent to that service.
Questions about this lesson
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