面向对象：添加删除和修改学生信息

package com.itheima.test7;

public class Test {
    public static void main(String[] args) {
        //定义一个长度为三的数组
        Student[] arr= new Student[3];
        //添加数据
        Student s1 = new Student(1,"lisa",25);
        Student s2 = new Student(2,"jisoo",26);
        //Student s3 = new Student(3,"rose",25);
        //赋值
        arr[0] = s1;
        arr[1] = s2;
        //arr[2] = s3;
        //1.添加一个对象
        Student s4 = new Student(4,"jennie",25);

        //唯一性判断,已存在，则不用添加
        boolean flag = contains(arr,s4.getId());
        if(flag){
            System.out.println("id重复");
        }else{
            //数组已满，创建新数组，新数组长度=老数组+1；
            //数组没满，直接添加    写成方法
            int count = getCount(arr);
            if(count== arr.length){
                //已经存满,将老数组传递给新数组
                Student[] newArr = createNewArr(arr);
                //count是填充新元素的索引
                newArr[count] = s4;
                //2.遍历所有学生信息
                printArr(newArr);
            }else{
                arr[count] = s4;
                printArr(arr);
            }

        }
    }

    //打印元素，需要新数组老数组都打印所以要写方法,只需要打印，返回值为空
    public static void printArr(Student[] arr){
        for (int i = 0; i < arr.length ; i++) {
            //数组要用变量接收
            Student stu = arr[i];
            if(stu!=null){
                System.out.println(stu.getId()+","+ stu.getAge()+","+stu.getName());
            }
        }
    }
    //创建新数组,返回的是Student[]类型的数组
    public static Student[] createNewArr(Student[] arr){
        Student[] newArr =new Student[arr.length+1];
        //循环遍历得到老数组中每一个元素
        for (int i = 0; i < arr.length; i++) {
            newArr[i] = arr[i];
        }
        return newArr;
    }

    //定义一个方法判断数组中存了几个元素
    public static int getCount(Student[] arr){
        //统计不为空的元素
        int count= 0 ;
        for (int i = 0; i < arr.length; i++) {
            if(arr[i]!=null){
                count++;
            }
        }
        return count;
    }

    //需要数组、id,需要判断是否存在，所以要返回,用boolean
    public static boolean contains(Student[] arr,int id){
        for (int i = 0; i < arr.length; i++) {
            //获取数组里的每一个学生对象
            Student stu = arr[i];
            if(stu != null){
                //null不能直接使用
                //获取数组中学生对象的id
                int sid = stu.getId();
                //比较
                if (sid == id){
                    return true;
                }
            }
        }
        //循环结束后未找到直接判断错误
        return false;
    }

}

package com.itheima.test7;

public class Test3 {
    public static void main(String[] args) {
        //定义一个长度为三的数组
        Student[] arr= new Student[3];
        //添加数据
        Student s1 = new Student(1,"lisa",25);
        Student s2 = new Student(2,"jisoo",26);
        Student s3 = new Student(3,"rose",25);
        //赋值
        arr[0] = s1;
        arr[1] = s2;
        arr[2] = s3;
        //3.通过id删除信息
        //如果存在，则删除，如果不存在，则提示删除失败
        int index = getIndex(arr, 4);
        if(index>=0){
            //如果存在则删除（索引置空）
            arr[index] = null;
            //遍历数组
            printArr(arr);
        }else{
            System.out.println("id不存在，删除失败");
        }
    }

    //判断是否存在，所以必须返回
    public static int getIndex(Student[] arr,int id){
        for (int i = 0; i < arr.length; i++) {
            //依次获得每一个学生对象
            Student stu = arr[i];
            //对stu进行一个非空判断
            if(stu!=null){
                int sid = stu.getId();
                if(sid == id){
                    return i;
                }
            }

        }
        //循环结束后还没找到
        return -1;
    }
    //打印元素，需要新数组老数组都打印所以要写方法,只需要打印，返回值为空
    public static void printArr(Student[] arr){
        for (int i = 0; i < arr.length ; i++) {
            //数组要用变量接收
            Student stu = arr[i];
            if(stu!=null){
                System.out.println(stu.getId()+","+ stu.getAge()+","+stu.getName());
            }
        }
    }
}

package com.itheima.test7;

public class Test4 {
    public static void main(String[] args) {

        Student[] arr= new Student[3];

        Student s1 = new Student(1,"lisa",25);
        Student s2 = new Student(2,"jisoo",26);
        Student s3 = new Student(3,"rose",25);

        arr[0] = s1;
        arr[1] = s2;
        arr[2] = s3;

        //id为2的年龄+1
        int index =getIndex(arr,2);

        //判断索引
        if(index>=0){
            //存在年龄+1
            Student s = arr[index];
            //把原来的年龄拿出来
            int newAge = s.getAge() + 1;
            //把+1之后的年龄塞回去
            s.setAge(newAge);
            printArr(arr);
        }else {
            System.out.println("不存在");
        }
    }
    //判断是否存在，所以必须返回
    public static int getIndex(Student[] arr,int id) {
        for (int i = 0; i < arr.length; i++) {
            //依次获得每一个学生对象
            Student stu = arr[i];
            //对stu进行一个非空判断
            if (stu != null) {
                int sid = stu.getId();
                if (sid == id) {
                    return i;
                }
            }
        }
        //循环结束后还没找到
        return -1;
    }

    //打印元素，需要新数组老数组都打印所以要写方法,只需要打印，返回值为空
    public static void printArr(Student[] arr){
        for (int i = 0; i < arr.length ; i++) {
            //数组要用变量接收
            Student stu = arr[i];
            if(stu!=null){
                System.out.println(stu.getId()+","+ stu.getAge()+","+stu.getName());
            }
        }
    }
}

package com.itheima.test7;

public class Student {
    private int id; //对字符串操作 先用int
    private String name;
    private int age;

    public Student() {
    }

    public Student(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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;
    }
}