static-静态方法和工具类

什么叫静态方法

特点和调用方式

• 工具类

  定义：帮助我们做一些事情的，但是不描述任何事物的类

  1. 已经学习过的类

  2. 工具类的使用规则

  3. 练习

     实操

     类--ArrayUtil

     package a02staticdemo2;
     public class ArrayUtil {
         //私有化构造方法
         //目的：为了不让外界创建他的对象
         private ArrayUtil(){}
     
         //需要定义为静态，方便使用
         public static String printArr(int[] arr){
             StringBuilder sb = new StringBuilder();
             sb.append('[');
             for (int i = 0; i < arr.length; i++) {
                 if (i<arr.length-1){
                     sb.append(arr[i]).append(",");
                 }else if (i==arr.length-1){
                     sb.append(arr[i]).append("]");
                 }
             }
             return sb.toString();
         }
         public static double getAverage(double[] arr){
             double sum = 0;
             for (int i = 0; i < arr.length; i++) {
                 sum = sum + arr[i];
             }
            return sum / arr.length;
         }
     }
     

     测试--TestDemo

     package a02staticdemo2;
     public class TestDemo {
         public static void main(String[] args) {
             //测试工具类中的两个方法
             int[] arr1 ={1,2,3,4,5};
             String str = ArrayUtil.printArr(arr1);
             System.out.println(str);//[1,2,3,4,5]
     
     
             double[] arr2 = {1.1,2.2,3.3,4.4,5.5};
             double average = ArrayUtil.getAverage(arr2);
             System.out.println(average);//3.3
         }
     }
     

  4. 练习2

     实操

     工具类--studentsArrayUtil

     package a03staticdemo3;
     import java.util.ArrayList;
     public class studentsArrayUtil {
         private studentsArrayUtil(){
     
         }
     
         public static int age(ArrayList<students> ast){
             int sum = 0;
             for (int i = 0; i < ast.size(); i++) {
                 int age = ast.get(i).getAge();
                 if (age>sum){
                     sum  = age;
                 }
             }
             return sum;
         }
     }
     

     学生类--students

     package a03staticdemo3;
     public class students {
         private String name;
         private int age;
         private String gender;
     
         public students() {
         }
     
         public students(String name, int age, String gender) {
             this.name = name;
             this.age = age;
             this.gender = gender;
         }
     
         public String getName() {
             return name;
         }
     
         public void setName(String name) {
             this.name = name;
         }
     
         public int getAge() {
             return age;
         }
     
         public void setAge(int age) {
             this.age = age;
         }
     
         public String getGender() {
             return gender;
         }
     
         public void setGender(String gender) {
             this.gender = gender;
         }
     }
     
     

     测试--studentsTest

     package a03staticdemo3;
     import java.util.ArrayList;
     import java.util.Scanner;
     
     public class studentsTest {
         public static void main(String[] args) {
             Scanner sc = new Scanner(System.in);
             ArrayList<students> ast = new ArrayList<>();
             for (int i = 0; i < 3; i++) {
                 System.out.println("请输入学生姓名");
                 String name = sc.next();
                 System.out.println("请输入学生年龄");
                 int age = sc.nextInt();
                 System.out.println("请输入学生性别");
                 String gender = sc.next();
                 students st = new students(name,age,gender);
                 ast.add(st);
             }
             int age = studentsArrayUtil.age(ast);
             System.out.println(age);
         }
     }