From 296031c5f5ab4d7eb28ffd40cadabf5727c65eb0 Mon Sep 17 00:00:00 2001
From: xuxin <840198532@qq.com>
Date: Wed, 28 Jan 2026 16:20:33 +0800
Subject: [PATCH] =?UTF-8?q?=E8=BF=9B=E9=98=B6day01-System=E7=B1=BB?=
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---
 .../src/com/inmind/system05/Demo21.java       | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 javaSE-day01/src/com/inmind/system05/Demo21.java

diff --git a/javaSE-day01/src/com/inmind/system05/Demo21.java b/javaSE-day01/src/com/inmind/system05/Demo21.java
new file mode 100644
index 0000000..2234a0c
--- /dev/null
+++ b/javaSE-day01/src/com/inmind/system05/Demo21.java
@@ -0,0 +1,32 @@
+package com.inmind.system05;
+
+import java.util.Date;
+
+/*
+System类
+    static long currentTimeMillis() 返回当前时间（以毫秒为单位）。
+    作用:测试一段代码的执行效率(io流的时候,检测普通流和高效流之间的效率问题)
+ */
+public class Demo21 {
+    public static void main(String[] args) {
+        //获取当前时间
+        long begin = System.currentTimeMillis();
+        System.out.println(begin);
+
+        //Date对象，无参构造，获取当前的毫秒值
+        /*Date date = new Date();
+        long time = date.getTime();
+        System.out.println(time);*/
+
+        for (int i = 0; i < 1000; i++) {
+            System.out.println(i);
+        }
+
+        long end = System.currentTimeMillis();
+        System.out.println("1000遍打印消耗的时间："+(end - begin));//毫秒级别
+
+        //我想要纳秒级别的时间差，怎么办？Instant
+        //如何获取2个Instant的纳秒间隔呢？Duration
+
+    }
+}