4.7稀疏数组

public static void main(String[] args) {
        int[][] array1 = new int[11][11];
        array1[1][2] = 1;
        array1[2][3] = 2;

        System.out.println("原始数组");

        for (int[] ints : array1) {
            for (int anInt : ints) {
                System.out.print(anInt + "\t");
            }
            System.out.println();
        }

        int sum = 0;
        for (int i = 0; i < 11; i++) {
            for (int j = 0; j < 11; j++) {
                if (array1[i][j] != 0){
                    sum++;
                }
            }
        }

        System.out.println("有效数组个数" + sum);

        //稀疏矩阵 array2【行数】【列数】【内容】
        int array2[][] = new int[sum+1][3];
        array2[0][0] = 11;
        array2[0][1] = 11;
        array2[0][2] = sum;
        int count = 0;
        for (int i = 0; i < array1.length; i++) {
            for (int j = 0; j < array1[i].length; j++) {
                if (array1[i][j] != 0){
                    count++;
                    array2[count][0] = i;
                    array2[count][1] = j;
                    array2[count][2] = array1[i][j];
                 }
            }
        }

        System.out.println("稀疏数组");
        for (int[] ints : array2) {
            for (int anInt : ints) {
                System.out.print(anInt + "\t");
            }
            System.out.println();
        }

        int[][] array3 = new int[array2[0][0]][array2[0][1]];
        for (int i = 1; i < array2.length; i++) {
            array3[array2[i][0]][array2[i][1]] = array2[i][2];
        }


        System.out.println("还原稀疏数组");
        for (int[] ints : array3) {
            for (int anInt : ints) {
                System.out.print(anInt + "\t");
            }
            System.out.println();
        }

    }

 五 面向对象OOP

5.1  方法回顾

方法的调用

public class Demo02 {
    public static void main(String[] args) {
        new Demo02().add(1,3);

    }

    public  int add(int a,int b){
        return a+b;
    }

public class Demo02 {
    public static void main(String[] args) {
        int add = Demo02.add(1, 3);//Demo02.add() alt+enter
        System.out.println(add);
    }

    public static int add(int a,int b){
        return a+b;
    }//静态方法 直接通过类.方法 调用

}

类

public class Demo01 {
    public static void main(String[] args) {
        Student student = new Student();  //new Student() alt+enter
        student.say();
    }
}

值传递 引用传递

//值传递
public class Demo03 {
    public static void main(String[] args) {
        int a= 1;
        System.out.println(a); //1
        change(a);
        System.out.println(a); //1
    }
    public static void change(int a){
        a = 10;
    }
}

//引用传递 对象 本质还是值传递
public class Demo04 {
    public static void main(String[] args) {
        Person person = new Person();
        //NEW 创建一个对象
        System.out.println(person.name); //null
        Demo04.change(person);
        System.out.println(person.name); //fxh
    }
    public static void change(Person person){
        //person是一个对象 指向的Person person = new Person(); 是一个具体的人 可以改变属性
        person.name = "fxh";
    }
}
//定义一个person类
class Person{
    String name;
}

 5.2 类与对象的创建