Lecture 1 - Introductions

https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/List.html

Functional Abstraction

Wrap behaviour into a function

double distanceBetween(double x1, double y1, double x2, double y2)

Data Abstraction

Wrap related data into a class

class Point {
    double x;
    double y;
    Point(double x, double y) {
        this.x = x;
        this.y = y;
    }
}

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Effect-Free Programming

Prevent side–efects by making Point immutable

class Point {
	final double x; // final modifier for one-time initialization
	final double y;
	
	Point(double x, double y) {
		this.x = x;
		this.y = y;
	}
}

Return new points

Point moveX(Point p, double dx) {
	return new Point(p.x + dx, p.y);
}

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Pipelining

p.moveX(1.0).moveY(1.0).distanceTo(new Point(1.0, 1.0))

Lists

• Lists are immutable

List<Double> list = List.of(1.0, 2.0, 3.0)

Loops

for (Point p : points) {
	do something
}

Streams

points.stream()
points.stream().map(p -> origin.distanceTo(p))
// p -> ... is a lambda expression

Interpretation vs Compilation

Developing a program: Editor (vim) → Compile → Run Quit Editor: ESC → : q (quit), : q! (force quit), : wq! Learn Editor: vimtutor

Compile code: javac Program.java Avoid AI: We don’t use nested classes and public

Run program: java DistanceCalculator (main method) jshell is the testing frame.

Getter

record IntPair(int x) {}
// an auto-generated getter is .x()