Java 面向对象进阶 02 static 静态方法和工具类（黑马）

工具类代码：

public class ArrayUtil {

    private ArrayUtil(){

    }

    public static String printArr(int [] arr){
        StringBuilder sb = new StringBuilder();
        sb.append("[");
        for(int i=0;i

public class TestDemo {
    public static void main(String[] args) {
        int  [ ]arr1 = {1,2,3,4,5};
        String str = ArrayUtil.printArr(arr1);
        System.out.println(str);

        double [] arr2 ={1.2,3.4,5.6};
        double d = ArrayUtil.getAverage(arr2);
        System.out.println(d);

    }
}

运行结果：

工具类的循环：

这样可以提高效率：

javabean 代码：

public class Student {
    private String name;
    private int age;
    private String gender;

    public Student() {
    }

    public Student(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;
    }

}

主函数代码：

import sun.security.util.ArrayUtil;

import java.util.ArrayList;

public class TestDemo {
    public static void main(String[] args) {
        ArrayList list =new ArrayList();
        int arr[]= {1,3,9,8,7};

        Student s1 = new Student("小明",20,"男");
        Student s2 = new Student("小花",22,"女 ");
        Student s3 = new Student("小刘",21,"男");

        list.add(s1);
        list.add(s2);
        list.add(s3);
        int maxAge = StudentUtil.maxAge(list);
        System.out.println(maxAge);
    }
}

学生类代码：

import java.util.ArrayList;

public class StudentUtil {

    private StudentUtil(){

    }

    public static int maxAge(ArrayList list){
        int  max = list.get(0).getAge();
        for(int i=1;i

代码结果：