在 Java 中懒惰地创建一个颜色映射

Question

我创建了一个函数来在 java 中创建颜色图。

final void setDefaultColourMap() {

        colourMap = new HashMap<>();

        colourMap.put(0, Color.BLACK);

        colourMap.put(1, Color.RED);

        colourMap.put(2, Color.GREEN);

        colourMap.put(3, Color.BLUE);

        colourMap.put(4, Color.PINK);

        colourMap.put(5, Color.YELLOW);

        colourMap.put(6, Color.CYAN);

        colourMap.put(7, Color.ORANGE);

        colourMap.put(8, Color.MAGENTA);

        colourMap.put(9, Color.DARK_GRAY);

        colourMap.put(10, Color.WHITE);

        colourMap.put(11, Color.GRAY);

        colourMap.put(12, Color.LIGHT_GRAY);

    }

我想创建一个 java 流，当请求颜色时，它会生成一个新的随机数并延迟返回一个随机颜色。

像惰性列表之类的东西。

编辑：

我读过函数式编程范式支持惰性列表。例如，有一个斐波那契数列的列表，该列表理论上存储列表中的所有元素，但实际上，会在请求时生成第 n 个元素。

我想用一些逻辑来模拟惰性颜色映射。我生成的颜色图只有 13 种颜色的输入。我不想手动输入高达一百左右的值。

我想模拟一个懒惰的彩色地图。因此，当我请求键为 35 的颜色时，colorMap 是用一些最多为 35 的随机颜色制定的，并返回第 35 个值。

我基本上只能返回 35 并存储它，但理想情况下，如果访问 35，在我的扩展程序中，您可以假设存在最大 35 的值。

Answer 1

这是一个开始：import java.awt.Color;import java.util.HashMap;import java.util.Random;public class Main {&nbsp; &nbsp; public static void main(String[] args) {&nbsp; &nbsp; &nbsp; &nbsp; ColorMap map = new ColorMap();&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(map.get(19));&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(map.get(9));&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(map.get(9));&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(map.get(0));&nbsp; &nbsp; &nbsp; &nbsp; for(int key : map.keySet()){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.println(key);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}class ColorMap extends HashMap<Integer, Color>{&nbsp; &nbsp; Random rand = new Random();&nbsp; &nbsp; @Override&nbsp; &nbsp; public Color get(Object key){&nbsp; &nbsp; &nbsp; &nbsp; if(! (key instanceof Integer)) return null;&nbsp; &nbsp; &nbsp; &nbsp; Color color = super.get(key);&nbsp; &nbsp; &nbsp; &nbsp; if(color == null){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; color = makeRandomColor();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; put((Integer) key,color);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return color;&nbsp; &nbsp; }&nbsp; &nbsp; private Color makeRandomColor(){&nbsp; &nbsp; &nbsp; &nbsp; return new Color( rand.nextFloat(), rand.nextFloat(), rand.nextFloat());&nbsp; &nbsp; }}编辑：要填充缺失值，您需要循环并检查所有先前值：import java.awt.Color;import java.util.HashMap;import java.util.Random;public class Main {&nbsp; &nbsp; public static void main(String[] args) {&nbsp; &nbsp; &nbsp; &nbsp; ColorMap map = new ColorMap();&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(map.get(19));&nbsp; &nbsp; &nbsp; &nbsp; for(int key : map.keySet()){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.println(key);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}class ColorMap extends HashMap<Integer, Color>{&nbsp; &nbsp; Random rand = new Random();&nbsp; &nbsp; @Override&nbsp; &nbsp; public Color get(Object key){&nbsp; &nbsp; &nbsp; &nbsp; if(! (key instanceof Integer)) return null;&nbsp; &nbsp; &nbsp; &nbsp; int positiveIntKey = Math.abs((Integer) key);&nbsp; &nbsp; &nbsp; &nbsp; Color color = super.get(positiveIntKey);&nbsp; &nbsp; &nbsp; &nbsp; if(color == null){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; fillMapUpTo(positiveIntKey);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return super.get(positiveIntKey);&nbsp; &nbsp; }&nbsp; &nbsp; private void fillMapUpTo(Integer positiveIntKey) {&nbsp; &nbsp; &nbsp; &nbsp; for(int key = 0; key <= positiveIntKey; key++){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if(super.get(key) == null){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; put(key,makeRandomColor());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }&nbsp; &nbsp; private Color makeRandomColor(){&nbsp; &nbsp; &nbsp; &nbsp; return new Color( rand.nextFloat(), rand.nextFloat(), rand.nextFloat());&nbsp; &nbsp; }}