學習筆記

承上篇：[JAVA]數值比大小之double[]

以下呈現幾種BigDecimal array比大小的寫法和速度

內容包含計算array中的加總sum，取最大max，取最小min，平均avg

速度是double3 > double2

array數值10萬筆，decimal2執行91 ms，decimal3執行32 ms

decimal2還有偷懶不算加總和平均，速度仍然筆decimal3還要慢

init array ----------------------
count = 100,000
Test2 ----------------------
sum = 0 , max = 1000.996076938839223657851107418537139892578125 , min = 1.0000248972125138635647090268321335315704345703125 , avg = 0
Time: 91 ms
Test3 ----------------------
sum = 50051208.58220991677612499159977232920937240123748779296875 , max = 1000.996076938839223657851107418537139892578125 , min = 1.0000248972125138635647090268321335315704345703125 , avg = 500.5120858220991677612499159977232920937240123748779296875
Time: 32 ms

程式如下 ：

import lombok.extern.slf4j.Slf4j;
import org.springframework.http.MediaType;

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.util.Arrays;
import java.util.Collections;

@Slf4j
public class DecimalArray {

    public static void main(String[] args) {

        System.out.println("init array ----------------------");
        int count = 100000;//可以指定要多少數量去比大小

        DecimalFormat df = new DecimalFormat("#,###");
        System.out.println("count = " + df.format(count));

        BigDecimal[] init_BigDecimal = new BigDecimal[count];
        for(int i = 0 ;i < count; i++){
            init_BigDecimal[i] = new BigDecimal(Math.random() *1000+1);
        }

        //array 0:max,1:min,2:avg
        BigDecimal[] result_Decimal = new BigDecimal[3];
        result_Decimal = decimal2( init_BigDecimal );
        result_Decimal = decimal3( init_BigDecimal );

    }

    public static BigDecimal[] decimal2(BigDecimal[] init ) {
        System.out.println("Test2 ----------------------");
        Long start = System.currentTimeMillis();
        BigDecimal sum = new BigDecimal(0) ;
        BigDecimal max = new BigDecimal(0) ;
        BigDecimal min = new BigDecimal(0) ;
        BigDecimal avg = new BigDecimal(0) ;
        BigDecimal[] result = new BigDecimal[3];
        int length = init.length;

        Arrays.sort(init);
        max = init[length-1];
        min = init[0];

        System.out.println(String.format("sum = %s , max = %s , min = %s , avg = %s",sum,max,min,avg));

        Long end = System.currentTimeMillis();
        System.out.println("Time: " + (end - start) + " ms");

        result[0] = max;
        result[1] = min;
        result[2] = avg;
        return result;
    }

    public static BigDecimal[] decimal3(BigDecimal[] init ) {
        System.out.println("Test3 ----------------------");
        Long start = System.currentTimeMillis();
        BigDecimal sum = new BigDecimal(0) ;
        BigDecimal max = new BigDecimal(0) ;
        BigDecimal min = new BigDecimal(0) ;
        BigDecimal avg = new BigDecimal(0) ;
        BigDecimal[] result = new BigDecimal[3];
        int length = init.length;
        Arrays.sort(init);
        for(int i = 0 ; i < length ; i++){
            if(i == 0){
                min = init[i];
            }

            sum = sum.add(init[i]);

            //max < init[i]
            if(max.compareTo(init[i]) == -1){
                max = init[i];
            }

            //min > init[i]
            if(min.compareTo(init[i]) == 1 ){
                min = init[i];
            }
        }

        avg = sum.divide(new BigDecimal(length));

        System.out.println(String.format("sum = %s , max = %s , min = %s , avg = %s",sum,max,min,avg));

        Long end = System.currentTimeMillis();
        System.out.println("Time: " + (end - start) + " ms");

        result[0] = max;
        result[1] = min;
        result[2] = avg;
        return result;
    }

}