目录
遍历数组
import java.util.Arrays;
public class Main {
public static void main(String[] args) {
int[] ns = { 1, 1, 2, 3, 5, 8 };
System.out.println(ns); // 类似 [I@7852e922
// 使用for循环可以遍历数组
for (int i = 0; i < ns.length; i++) {
int n = ns[i];
System.out.println(n);
}
// for each循环直接遍历数组的元素
for (int n : ns) {
System.out.println(n);
}
System.out.println(Arrays.toString(ns));
}
}
数组排序
import java.util.Arrays;
public class Main {
public static void main(String[] args) {
/**
* 冒泡法
*/
int[] ns = { 28, 12, 89, 73, 65, 18, 96, 50, 8, 36 };
// 排序前:
System.out.println(Arrays.toString(ns));
// 排序:
for (int i = 0; i < ns.length; i++) {
for (int j = i + 1; j < ns.length; j++) {
if (ns[i] > ns[j]) {
// 交换ns[i]和ns[j]:
int tmp = ns[j];
ns[j] = ns[i];
ns[i] = tmp;
}
}
}
// 排序后:
System.out.println(Arrays.toString(ns));
/**
* 使用Arrays.sort
*/
int[] ns1 = { 28, 12, 89, 73, 65, 18, 96, 50, 8, 36 };
// 排序前:
System.out.println(Arrays.toString(ns1));
// 排序
Arrays.sort(ns1);
// 排序后:
System.out.println(Arrays.toString(ns));
}
}
二维数组
import java.util.Arrays;
public class Main {
public static void main(String[] args) {
int[][] stds = {
// 语文, 数学, 英语, 体育
{ 68, 79, 95, 81 }, { 91, 89, 53, 72 }, { 77, 90, 87, 83 }, { 92, 98, 89, 85 }, { 94, 75, 73, 80 } };
System.out.println(stds.length);
System.out.println(Arrays.toString(stds));
System.out.println(Arrays.deepToString(stds));
// TODO: 遍历二维数组,获取每个学生的平均分:
for (int[] std : stds) {
int sum = 0;
for (int s : std) {
sum = sum + s;
}
int avg = sum / std.length;
System.out.println("Average score: " + avg);
}
// TODO: 遍历二维数组,获取语文、数学、英语、体育的平均分:
int[] sums = { 0, 0, 0, 0 };
for (int[] std : stds) {
sums[0] = sums[0] + std[0];
sums[1] = sums[1] + std[1];
sums[2] = sums[2] + std[2];
sums[3] = sums[3] + std[3];
}
System.out.println("Average Chinese: " + sums[0] / stds.length);
System.out.println("Average Math: " + sums[1] / stds.length);
System.out.println("Average English: " + sums[2] / stds.length);
System.out.println("Average Physical: " + sums[3] / stds.length);
}
}
命令行参数
命令行参数是String[]
命令行参数由JVM接收用户输入并传给main方法
如何解析命令行参数由程序自己实现
public class Main {
public static void main(String[] args) {
System.out.println("Number of args: " + args.length);
for (String arg : args) {
if ("-version".equals(arg))
System.out.println("version 1.0");
}
}
}