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+```java
+import java.util.Scanner;
+//.编写函数，计算圆的面积和周长，在主函数中接受圆的半径，在自定义函数中计算并输出
+public class D1 {
+    public static void main(String[] args) {
+        Scanner sc =new Scanner(System.in);
+        System.out.println("请输入 圆的半径");
+        double radius= sc.nextDouble();
+        System.out.println("圆的周长："+ perimeter(radius));
+        System.out.println("圆的面积："+area(radius));
+    }
+    public static double perimeter(double radius){
+     return 2*3.1415926*radius; //计算圆的周长
+
+    }
+    public static double area(double radius){
+        return 3.1415926*radius*radius;//计算圆的面积
+    }
+}
+```
+
+```java
+import java.util.Arrays;
+import java.util.Random;
+import java.util.Scanner;
+
+//在主函数中产生20个0-10之间的随机数，将这20个随机数存入数组，并通过函数计算某个数在这些随机数中出现的次数（这“某个数”是在主函数中由用户输入的）
+public class D2 {
+    public static void main(String[] args) {
+        Random ra = new Random();
+        int num = ra.nextInt(10);
+        long[] numberm = new long[20];
+        for(int i = 0; i < 20; i++) {
+          numberm[i]=num;
+            Scanner sc=new Scanner(System.in);
+            System.out.println("请输入某个数");
+            long nums= sc.nextLong();
+
+        }
+
+                }
+    public static void seach(long[] numberm,long nums){
+        int count=0;
+        for (int i=0; i<numberm.length;i++){
+            if (nums==numberm[i]){
+                count++;
+            }
+        }
+        System.out.println("次数："+count);
+    }
+}
+
+```
+
+~~~java
+用自定义函数是实现求某数组元素的和（大小不固定）
+
+```java
+package 方法;
+
+import java.util.Random;
+
+public class D3 {
+    public static void main(String[] args) {
+        Random r = new Random();
+        int nums[] = new int[8];
+        for (int i = 0 ; i < nums.length ; i ++) {
+            nums[i] = r.nextInt(90)+10;
+        }
+        System.out.print("随机数组为：");
+        for (int i = 0 ; i < nums.length ; i ++) {
+            System.out.print(nums[i] + " ");
+        }
+        System.out.println();
+        System.out.print("这几个数的和为：" + sum(arr));
+    }
+    public static int sum(int nums[]){
+        int num = 0;
+        for (int i = 0 ; i < arr.length ; i++) {
+            num += arr[i];
+        }
+        return num;
+    }
+}
+```
+~~~
+
+```java
+public class D4 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("请输入n的值：");
+        double num = sc.nextInt();
+        System.out.println("1!+(1!+2!)+(1!+2!+3!)+....+(1!+2!...+"+num+"+!)= "+ sum(num));
+    }
+    public static double  sum(double num) {
+        double sum = 0;
+        for (int a = 1 ; a <= num ; a ++) {
+            for (int j = 1 ; j <= a ; j ++) {
+                sum += j;
+            }
+        }
+        return sum;
+    }
+}
+```
+