Java application code execution time-consuming to detect anonymous function

package com.company.Util;

public class Times {
    public interface Block{
        void execute();
    }

    public static void  test(Block block)  {
        long begin =System.currentTimeMillis();
        block.execute();
        long end = System.currentTimeMillis();
        double duration = (end-begin)/1000.0;
        System.out.println("耗时："+duration+"s");
    }
}

package com.company;

import com.company.Util.Times;

public class Main {
    public static void main(String[] args) {
        Times.test(new Times.Block() {
            @Override
            public void execute() {
                StringBuilder j = new StringBuilder();
                for (int i = 0; i < 10000; i++) {
                    j.append(i);
                }
            }
        });
    }
}