计数ArrayList中的数字在一定范围内

Question

我正在添加用户输入的几个数字并将它们添加到数组列表中.

我的代码到目前为止:

package project143;

import java.util.*;

/**
 * @author --
 */
public class Histogram {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        // Input for grades
        int mark = 0;
        List<Integer> list = new ArrayList<Integer>();
        while (mark >= 0 && mark <= 100) {
            System.out.println("Enter students mark:");
            mark = input.nextInt();

            if (mark >= 0 && mark <= 100) {
                list.add(mark);
            }

        }
        System.out.println(list);
    }
}

现在,我需要计算list以下范围内的数量(0-29,30-39,40-69,70-100)

一旦我知道每个范围内有多少个数字,我需要在每个范围旁边显示" ",例如,在0到29范围内有10个数字,因此我需要显示10颗星(***).

我怎样才能做到这一点？

Answer 1

如果使用Eclipse Collections,则可以编写以下代码.首先,我们设置您指定的范围:

private ImmutableList<Interval> ranges = Lists.immutable.with(
    Interval.fromTo(0, 29),
    Interval.fromTo(30, 39),
    Interval.fromTo(40, 69),
    Interval.fromTo(70, 100));

然后我们可以使用匿名内部类在示例中使用这些范围.

final MutableBag<Interval> countByRange = Bags.mutable.empty();
Interval inputs = Interval.from(5).to(100).by(5);
inputs.forEach(new IntProcedure()
{
    public void value(final int grade)
    {
        countByRange.add(ranges.detect(new Predicate<Interval>()
        {
            public boolean accept(Interval range)
            {
                return range.contains(grade);
            }
        }));
    }
});
countByRange.forEachWithOccurrences(new ObjectIntProcedure<Interval>()
{
    public void value(Interval range, int occurrences)
    {
        System.out.println(range + " : " + StringIterate.repeat('*', occurrences));
    }
});

您需要将Interval输入替换为实际输入(在您的示例中为Scanner).我只想要一组简单的输入来测试.

代码输出如下:

Interval from: 70 to: 100 step: 1 size: 31 : *******
Interval from: 40 to: 69 step: 1 size: 30 : ******
Interval from: 30 to: 39 step: 1 size: 10 : **
Interval from: 0 to: 29 step: 1 size: 30 : *****

使用Java 8 Lambda语法,您可以编写以下内容:

MutableBag<Interval> countByRange = Bags.mutable.empty();
Interval inputs = Interval.from(5).to(100).by(5);
inputs.forEach((int grade) -> {
    countByRange.add(ranges.detect(range -> range.contains(grade)));
});
countByRange.forEachWithOccurrences((range, occurrences) ->
    {System.out.println(range + " : " + StringIterate.repeat('*', occurrences));});

如果您想尝试使用collect而不是使用forEach添加到包中,以下代码会产生相同的结果.

Interval.from(5).to(100).by(5)
    .collect(grade -> ranges.detect(range -> range.contains(grade)))
    .toBag()
    .forEachWithOccurrences((range, occurrences) ->
        {System.out.println(range + " : " + StringIterate.repeat('*', occurrences));});

注意:我是Eclipse集合的提交者.