什么是runtime

定义

In computer programming, a runtime library is a special program library used by a compiler, to implement functions built into a programming language, during the runtime (execution) of a computer program. This often includes functions for input and output, or for memory management.
在计算机编程中，runtime是在代码的执行过程中，编译器实现编程语言函数功能所依赖的一个特殊的库，通常包含基础输入输出功能和内存管理。

示例

public static void main (String args[]){
    System.out.println("hello world");
}

在上述代码中，我们仅仅告诉计算机要在屏幕上显示"hello world"字样，但具体怎么显示，第一步怎么做，第二步怎么做，都需要调用runtime已经封装好的函数去实现。

参考链接:https://stackoverflow.com/questions/3900549/what-is-runtime