What does timestamp mean in java

The timestamp in Java represents the number of milliseconds that have passed since 1970. The types include the current timestamp (System.currentTimeMillis()) and the specified timestamp (Instant.ofEpochMilli(long millis)). Can be converted to a readable string through the SimpleDateFormat class and used in logging events, sorting, creating unique identifiers, caches, and databases.

Time stamp in java

Time stamp in Java represents the since Unix epoch (January 1, 1970 The number of milliseconds since 00:00:00 GMT). It is a long (64-bit) number used to accurately record the time an event occurred.

Types and acquisition methods

There are two main types of timestamps in Java:

• Current timestamp: Use the System.currentTimeMillis() method to obtain and return the number of milliseconds since the Unix epoch of the current system time.
• Specified timestamp: You can use the Instant.ofEpochMilli(long millis) method to create a specified timestamp. The millis parameter represents the number of milliseconds elapsed since the Unix epoch.

Conversion and formatting

Time stamps can be converted into readable time strings through the SimpleDateFormatter class. For example:

<code class="java">SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String formattedDate = sdf.format(new Date(timestamp));</code>

Uses

Time stamps in Java have a wide range of uses, including:

• Recording the time when an event occurs
• Comparison and sorting events
• Create unique identifiers (such as IDs)
• For caching and database use

Usage examples

The following example shows how to use timestamps in Java:

<code class="java">// 获取当前时间戳
long currentTimeMillis = System.currentTimeMillis();

// 创建指定时间戳（2023年1月1日00:00:00 GMT）
long epochMillis = 1640995200000L;
Instant instant = Instant.ofEpochMilli(epochMillis);

// 转换时间戳为字符串
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String formattedDate = sdf.format(new Date(currentTimeMillis));</code>

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