求平均值，方差，中位数（不高于两位小数）

心已赠人 2022-06-01 12:28 206阅读 0赞

package com.math;
    
    import java.text.DecimalFormat;
    import java.util.ArrayList;
    
    public class Math {
    
    	public Math(){}
    	
    	/****
    	 * @comments 计算一个list中的平均值
    	 * @param list
    	 * @return 返回不高于两位小数的平均值
    	 */
    	public String getAverage(ArrayList<Long> list) {
    		DecimalFormat df= new DecimalFormat("#.##");
    		long sum = 0;
    		for(int i =0;i<list.size();i++) {
    			sum = sum + list.get(i);
    		}
    		double d= (double)sum/(double)list.size();
    		String avg = df.format(d);
    		System.out.println("平均值为："+avg);
    		return avg;
    	}
    	
    	/****
    	 * @comments 求一组数的中位数
    	 * @param list
    	 * @return 返回不高于两位小数的中位数
    	 */
    	public String getMedian(ArrayList<Long> list) {
    		DecimalFormat df = new DecimalFormat("#.##");
    		double d = 0;
    		long[] l = new long[list.size()];
    		int t=0;
    		while(!list.isEmpty()){
    			long min = list.get(0);
    			for(int i=1;i<list.size();i++) {
    				if(min>list.get(i))
    					min=list.get(i);
    			}
    			l[t]=min;
    			list.remove(min);
    			t++;
    		}
    		if(t%2==0) {
    			d=l[(t/2)-1]+l[t/2];
    			d=d/2;
    		}else
    			d = l[t/2];
    		String med = df.format(d);
    		System.out.println("中位数："+med);
    		return med;
    	}
    	/****
    	 * @comments 求list的方差
    	 * @param list
    	 */
    	public void getVariance(ArrayList<Long>list) {
    		DecimalFormat df = new DecimalFormat("#.##");
    		String strVar = "";
    		double sum = 0;
    		for(int i=0;i<list.size();i++) {
    			sum = sum + list.get(i);
    		}
    		double avg = sum/(double)list.size();
    		double var = 0;
    		int listSize = list.size();
    		for(int i=0;i<listSize;i++) {
    			var = var+(list.get(i)-avg)*(list.get(i)-avg);
    		}
    		var = var/listSize;
    		strVar = df.format(var);
    		System.out.println("方差为:"+strVar);
    	}
    	/***
    	 * @comments test用例
    	 * @param args
    	 */
    	public static void main(String[] args) {
    		Math math = new Math();
    		long[] test = {50,60,100,58,68,89,90};
    		ArrayList<Long>list = new ArrayList<Long>();
    		for(int i=0;i<test.length;i++) {
    			list.add(test[i]);
    		}
    		math.getAverage(list);
    		//由于在求中位数时，把list清空，为了方便，先求方差
    		math.getVariance(list);
    		math.getMedian(list);
    	}
    }