What is java timer expression

The timer expression is used to define the execution plan of the task. The timer expression is based on the model of "execute a task after a given time interval". The expression usually consists of two parts: an initial delay and a time interval.

Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Java timers (Timer) and timer tasks (TimerTask) provide a way to schedule the execution of single or recurring scheduled tasks in the future. The timer expression is used to define the execution plan of the task.

The expression of the timer is based on the model of "executing a task after a given time interval". The expression usually consists of two parts: an initial delay and a time interval.

The following are examples of some commonly used timer expressions:

1. Start after an initial delay, and then execute at fixed intervals:

java

new Timer().schedule(task, delay, period);

Where:

task is the timer task to be executed.

delay is the initial delay (in milliseconds) after which the task will start executing.

period is the fixed time interval (in milliseconds) for task execution.

2. Execute only once after a given initial delay:

java

new Timer().schedule(task, delay);

Where:

task is the timer task to be executed.

delay is the initial delay in task execution in milliseconds.

3. Continuous execution until canceled:

java

new Timer().schedule(task, 0);

Where:

task is the timer task to be executed.

0 means that the task will start executing immediately and will continue to execute until canceled.

4. Use cron expressions for more complex plans:

Java's Quartz library provides cron expressions for defining more complex task scheduling plans. Quartz's cron expression contains 6 or 7 fields, representing seconds, minutes, hours, date, month, week, and year (optional).

For example, the following is an example of a Quartz cron expression, indicating that the task will be executed at 10 am every day:

java

String cronExpression = "0 0 10 * * ?"; // 每小时的第10分钟执行一次，每天重复。

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