In Java, use the currentTimeMillis() method of the System class to obtain the millisecond representation of the current system time.

Use the currentTimeMillis() method of the System class in Java to obtain the millisecond representation of the current system time

The System class is an important class in Java, which provides some system-related methods and properties. Among them, the currentTimeMillis() method is a static method in the System class, used to obtain the millisecond representation of the current system time. This article will introduce how to use this method to obtain the system time.

First of all, we need to understand the specific usage of the System.currentTimeMillis() method. This method returns the millisecond representation of the current system time, which is the total number of milliseconds since midnight on January 1, 1970 to the current time. The return value type is long.

The following is a sample code that demonstrates how to use the System.currentTimeMillis() method to obtain the current system time:

public class GetCurrentTime {
    public static void main(String[] args) {
        // 获取当前系统时间的毫秒表示形式
        long currentTime = System.currentTimeMillis();
        
        // 输出当前系统时间的毫秒表示形式
        System.out.println("当前系统时间的毫秒表示形式：" + currentTime);
    }
}

The above code first calls the System.currentTimeMillis() method to obtain the milliseconds of the current system time. representation and assign the result to the variable currentTime. Then, the value of currentTime, which is the millisecond representation of the current system time, is output through the System.out.println() method.

Run the above code, we can get output similar to the following:

当前系统时间的毫秒表示形式：1623021775123

As you can see, the output result is a large number, indicating that the current system time is from January 1, 1970 The number of milliseconds to midnight. Note that this value is increasing as time passes.

In actual development, the System.currentTimeMillis() method can be used to easily obtain the current system time, especially for calculating the execution time of a certain code block, generating a unique timestamp, etc.

In addition to the System.currentTimeMillis() method, Java also provides other methods for obtaining system time, such as the System.nanoTime() method, the getTime() method in the Date class, etc. Each method has its own characteristics and applicable scenarios, and we can choose the appropriate method according to actual needs.

To summarize, this article introduces the use of the currentTimeMillis() method of the System class in Java to obtain the millisecond representation of the current system time. Through this method, we can easily obtain the current system time and time-related operations. In actual development, choosing the appropriate time acquisition method according to needs can better meet the needs.

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