如何在不创建额外实例变量的情况下创建对象数组？

Question

我正在尝试解决以下问题：

Implement a class called TriangleArray which has the following: No other instance variables or constants allowed.

An instance variable called list which is an array of Triangle objects.

No other instance variables or constants allowed.

Only one constructor which has two integer parameters. The first parameter called number is the length of list. The second parameter called maxSize is the maximum size allowed for the

The constructor initializes list to an array of Triangle objects.

The sides of each Triangle object are randomly generated integers in the range from 1 to maxSize.

Getter and setter methods for list.

A largest method with no parameters. The method returns the largest Triangle in list.

A toString method which returns a description of each Triangle in list.

如何在不使用其他实例变量的情况下填充充满随机对象的列表？

这是我目前的代码：

import java.util.Random;
public class TriangleArray
{
  private Triangle[ ] list;
  // list is an array of "number" Triangle objects.   
  // The maximum size of each Triangle edge is "maxSize".
  public TriangleArray (int number,  int maxSize);
  {
    list = new Triangle[number];

Answer 1

您可以使用函数中的局部变量来做到这一点。

public TriangleArray (int number,  int maxSize) {
    list = new Triangle[number];
    Random random = new Random();
    for(int i = 0; i < number; list[i] = makeRandomTriangle(random, maxSize);
}

private function makeRandomTriangle(Random random, int maxSize) {
    int a = random.nextInt(maxSize) + 1,
        b = random.nextInt(maxSize) + 1;

    // |a - b| <= c <= (a + b) because of the triangle inequality
    int min = Math.max(a - b, b - a),
        max = Math.min(maxSize, a + b);
    int c = rand.nextInt((max - min) + 1) + min;
    new Triangle(a, b, x);
}

Answer 2

实例变量或字段与局部变量不同。

参见：What is the difference between a local variable, an instance field, an input parameter, and a class field?

您可以很好地使用局部变量，例如：

public TriangleArray (int number,  int maxSize) {
  list = new Triangle[number];
  for(int i = 0; i < number; i++) {
    list[i] = makeTriangle(maxSize);
   }
}

private makeTriangle(maxSize) {
  Random r = new Random();

  do {
    int first = r.nextInt(maxSize - 1) + 1;
    int second = r.nextInt(maxSize - 1) + 1;
    int third = r.nextInt(maxSize - 1) + 1;

    int max = Math.max(first, Math.max(second, third));
  } while ((2 * max) - first - second - third) > 0);

  return new Triangle(first, second, third);
}

在此代码中，您永远不会创建新的实例变量。

Answer 3

您不需要使用实例变量来填充随机数。您可以使用 java.util.Random 或 Math.random:

list = new Triangle[number];
for (int i = 0; i < list.length; i++) {
    int a = (int)(Math.random() * (maxSize + 1));
    int b = (int)(Math.random() * (maxSize + 1));
    int c = (int)(Math.random() * (maxSize + 1));

    //handle the triangle inequality:
    while (c > a + b || c < Math.abs(a - b)) {
        c = (int)(Math.random() * (maxSize + 1));
    }

    list[i] = new Triangle(a, b, c);
}

Answer 4

假设 Triangle 对象的构造函数如下所示：

public Triangle(int a, int b, int c) { ...

我们初始化数组：

Random r = new Random(); // random number gen
for ( int i = 0; i < number; i++ ) {
  int a = r.nextInt(maxSize-1) + 1; // randomly generate each side
  int b = r.nextInt(maxSize-1) + 1;
  int c = r.nextInt(maxSize-1) + 1; // this won't necessarily make a proper triangle
  list[i] = new Triangle(a, b, c);
}

我们必须创建一个随机数生成器，然后我们必须遍历整个未创建的三角形数组并创建它们。迭代时，我们随机生成每条边 a、b、c，从 1 到 maxSize 的数字，然后在当前索引处创建 Triangle 对象。

list 是您的实例变量，同时变量 a、b、c 和 r 都是构造函数或您放入的任何函数的局部变量。

如何在不创建额外实例变量的情况下创建对象数组？

How can I create an array of objects without creating extra instance variables?

java

arrays

instance-variables

实例变量或字段与局部变量不同。