so the question basically says to Use a for loop to add 10 Circles to the ArrayList each with a random radius in the range of 2-5 and Print a table of all of the Circles in the ArrayList. You can use System.out.println(String.format("%.3f", this.getRadius)); to print the circle dimensions to 3 decimal places. but how does this work.
public class CirclesDriver
{
public static void main(String[] args) {
Random rand = new Random();
// ** Variables constants and objects **
Scanner scanner = new Scanner(System.in);
ArrayList<Circle> circles = new ArrayList<>();
// ** load the array list with circles **
for (int i = 0; i <= 10; i ) {
Circle circle = new Circle();
double radius = rand.nextDouble(5) 2;
}
// print the whole list
System.out.println("--------------------------------\n");
// ** Make sure your Circle class and ArrayList work with the following driver code **
System.out.println();
Circle c1 = new Circle();
System.out.println("C1: " c1.getID());
System.out.println("Radius: " c1.getRadius());
System.out.println("--------------------------------\n");
c1.setRadius(1.5);
System.out.println("C1: " c1.getID());
System.out.println("Radius: " c1.getRadius());
System.out.println("Area: " c1.getArea());
System.out.println("--------------------------------\n");
circles.get(3).setRadius(2.2);
System.out.println("C1: " circles.get(3).getID());
System.out.println("Radius: " circles.get(3).getRadius());
System.out.println("Diameter: " circles.get(3).getDiameter());
System.out.println("--------------------------------\n");
Circle c2 = circles.remove(9);
System.out.println("C2: " c2.getID());
System.out.println("Radius: " c2.getRadius());
System.out.println("Circumference: " c2.getCircumference());
System.out.println("--------------------------------\n");
// ** output
// ** closing message **
System.out.println("\nend of program");
CodePudding user response：
Based on the question, given code doesn't work. Here is the complete code and corresponding output.
import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;
public class CirclesDriver {
public static void main(String[] args) {
Random rand = new Random();
// ** Variables constants and objects **
Scanner scanner = new Scanner(System.in);
ArrayList<Circle> circles = new ArrayList<>();
// ** load the array list with circles **
for (int i = 1; i <= 10; i ) {
String id = "C" i;
double random = rand.nextDouble();
double radius = 2 (random * (5 - 2));
Circle circle = new Circle(id, radius);
circles.add(circle);
}
// print the whole list
System.out.println("--------------------------------\n");
// ** Make sure your Circle class and ArrayList work with the following driver code **
for(int i=0; i<circles.size(); i ) {
Circle circle = circles.get(i);
System.out.println();
System.out.println("C1: " circle.getId());
System.out.println("Radius: " String.format("%.3f", circle.getRadius()));
System.out.println("Diameter: " String.format("%.3f", circle.getDiameter()));
System.out.println("Circumference: " String.format("%.3f", circle.getCircumference()));
System.out.println("Area: " String.format("%.3f", circle.getArea()));
System.out.println();
}
}
}
class Circle {
private String id;
private double radius = 0;
public Circle(String id, double radius) {
this.id = id;
this.radius = radius;
}
public String getId() {
return id;
}
public double getRadius() {
return radius;
}
public double getDiameter() {
return radius * 2;
}
public double getArea() {
return 2 * 3.14 * radius * radius;
}
public double getCircumference() {
return 2 * 3.14 * radius;
}
}
Output
--------------------------------
C1: C1
Radius: 4.740
Diameter: 9.481
Circumference: 29.770
Area: 141.121
C1: C2
Radius: 3.677
Diameter: 7.353
Circumference: 23.089
Area: 84.886
C1: C3
Radius: 4.333
Diameter: 8.665
Circumference: 27.209
Area: 117.888
C1: C4
Radius: 4.592
Diameter: 9.184
Circumference: 28.838
Area: 132.423
C1: C5
Radius: 4.468
Diameter: 8.937
Circumference: 28.062
Area: 125.393
C1: C6
Radius: 3.024
Diameter: 6.047
Circumference: 18.988
Area: 57.413
C1: C7
Radius: 3.628
Diameter: 7.256
Circumference: 22.783
Area: 82.656
C1: C8
Radius: 2.086
Diameter: 4.173
Circumference: 13.103
Area: 27.339
C1: C9
Radius: 2.447
Diameter: 4.894
Circumference: 15.368
Area: 37.610
C1: C10
Radius: 4.301
Diameter: 8.602
Circumference: 27.010
Area: 116.172
CodePudding user response：
Pass radius to constructor
Simpler to define a constructor that takes the radius as an argument.
Define your Circle class. If the main purpose of your class is to communicate data transparently and immutably, write your class as a record. With a record, the compiler by default implicitly creates the constructor, getters, equals & hashCode, and toString. You can declare a record locally (within a method), or separately.
record Circle ( double radius ) {}
A DoubleStream can create a series of randomly generated double values. (The following code is untested)
List< Circle > circles =
ThreadLocalRandom
.current() // Returns a `ThreadLocalRandom `.
.doubles(
10L, // streamSize
2.0d, // randomNumberOrigin
5.0d // randomNumberBound
) // Returns a `DoubleStream`.
.mapToObj( double d -> return new Circle( d ) ) // Generates a stream of `Circle` objects.
.toList() // Returns a `List`.
;
We might be able to reduce .mapToObj( double d -> return new Circle( d ) ) with .mapToObj( Circle :: new ), a method reference referring to the constructor.
For output, loop the list. Add methods to the Circle class to return diameter and circumference.