Question One
编写一个应用程序，输出100以内的全部偶数，并以10个一行的形式输出。
public class Main{public static void main(String[] args){int cnt = 0;for(int i = 2; i <= 100; i += 2){cnt ++;System.out.print(i);if(cnt % 10 != 0) System.out.print(' ');else System.out.println();}}
}
Question Two
声明一些变量类型，用作练习
public class Main{public static void main(String[] args){byte a1 = 0x55;byte a2 = 95;System.out.println(a1 + " " + a2);short b = 0x55ff;System.out.println(b);int i = 1000;long l1 = 0xffff;long l2 = 2147483648L;System.out.println(l1 + " " + l2);char c = 'a';float f = 0.23F;System.out.println(f);double d1 = 0.007;double d2 = 0.7E-3;System.out.println(d1 + " " + d2);boolean fg = false;String s = "123";}
}
Question Three
练习 switch 语句语法
import java.util.Scanner;public class Main{public static void main(String[] args){Scanner sc = new Scanner(System.in);int x = sc.nextInt();switch (x * 2) {case 2 :System.out.println("Case One");break;case 3 :System.out.println("case Two");break;case 4 :System.out.println("case Three");break;default :System.out.println("case Four");break;}}
}
Question Four
随机数生成练习
public class Main{public static void main(String[] args){for(int i = 1; i <= 10; i ++){int num = (int)(100 * Math.random());System.out.print(num + " ");}System.out.println();for(int i = 1; i <= 10; i ++){// Random 生成 [0, 1) 的浮点数double num = Math.random();System.out.print(num + " ");}}
}
Question Five
输入 5 个整数求平均值
import java.util.Scanner;public class Main{public static void main(String[] args) {Scanner sc = new Scanner(System.in);double[] d = new double[5];double avg = 0.0d;for(int i = 0; i < 5; i ++){System.out.println("请输入第" + (i + 1) + "个整数: ");d[i] = sc.nextDouble();avg += d[i];}System.out.println("平均分数是: " + avg / 5.0);}
}
注意 : (同 C++ 的除法运算法则)
System.out.println(5 / 3); // 1
System.out.println(5.0 / 3); // 1.6666666666666667
Question Six
保留指定小数位数
import java.util.Scanner;public class Main{public static void main(String[] args) {System.out.printf("Two decimal places : %.2f", 5.0 / 3); // 1.6666666666666667System.out.printf("%n");System.out.printf("Three decimal places : %.3f", 5 / 3.0);}
}
Question Seven
GUI 实现 a + b，加入异常抛出
import javax.swing.*;public class Main {public static void main(String[] args) {try {// 用InputDialog获取用户输入的第一个数字int num1 = Integer.parseInt(JOptionPane.showInputDialog("Input first number:"));// 用InputDialog获取用户输入的第二个数字int num2 = Integer.parseInt(JOptionPane.showInputDialog("Input second number:"));// 计算两个数字的和int sum = num1 + num2;// 显示结果，使用INFORMATION_MESSAGE以显示信息图标JOptionPane.showMessageDialog(null, "Sum is " + sum,"Result", JOptionPane.INFORMATION_MESSAGE);}catch (NumberFormatException e) {// 捕获NumberFormatException并显示错误消息JOptionPane.showMessageDialog(null, "Invalid input. " +"Please enter a valid integer.", "Error", JOptionPane.ERROR_MESSAGE);}}
}
Question Eight
编写一个函数fun，它的功能是：求出1000以内能被7或11整除，但不能同时被7和11整除的数，存放到数组myarray中，fun函数返回该数组。在main()函数中输出该数组中的所有元素。
public class Main{public static void main(String[] args) {for(var x : fun()){System.out.print(x + " ");}}public static int[] fun(){int cnt = 0;int[] arr = new int[100];for(int i = 1; i <= 100; i ++){if((i % 7 == 0 || i % 11 == 0) && (i % 77 != 0)){arr[cnt ++] = i;}}return java.util.Arrays.copyOf(arr, cnt);}
}
需要注意 :
1. 如果想直接返回数组，这样写 : return new int[] {1, 2, 3}; 不需要指定长度
2. 返回子数组这样写，return java.util.Arrays.copyOf(arr, cnt)
Question Nine
区间复制部分数组 + 顺便实现 9*9 Multiplication
import java.util.Arrays;
public class Main{public static void main(String[] args) {int[] arr = new int[] {1, 2, 3, 4, 5, 6, 7, 8};for(int x : arr){System.out.print(x + " ");}System.out.println();int[] part = Arrays.copyOfRange(arr, 1, 4);System.out.println(Arrays.toString(part));Multiplication();}public static void Multiplication(){for(int i = 1; i <= 9; i ++){for(int j = 1; j <= i; j ++){System.out.print(i + "*" + j + "=" + (i * j));if(j == i) System.out.println();else System.out.print(" ");}}}
}
)
