23_API_System

 1.定义

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 2.构造方法

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 3.成员方法

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4.System类代码案例

package JavaBasicReview;


import java.util.Arrays;

public class JavaGrammer {
    public static void main(String[] args) {
        //创建System对象，构造器(private System() {})
        //currentTimeMillis,获取当前系统当前时刻的毫秒值，常用来计算程序的运行时常
        long time1 = System.currentTimeMillis();
        System.out.println(time1);
        //arraycopy,复制数组
        int[] arr = {1,2,3,4,5};
        int[] newarr = new int[2];
        System.arraycopy(arr,2,newarr,0,2);
        System.out.println(Arrays.toString(newarr));
    }
}