java study notes (d) multi-dimensional arrays

Two-dimensional array

0. Array Features

Is a reference to the array type itself
must specify the length of time a statement once it is determined to change can not happen again

1. Definition / Statement

Type stored inside [the name of the array;
int [] [] arrray;

2. Initialize

Static - all elements having a length
　　 int [] [] array = [ {1,2,3}, {4,5,6,7}, {7,8,9}};
dynamic element length is not only ---- (default);
　　 int [] [] Array = new new [. 3] [2];
　　 Array -> {{X, X}, {X, X}, {X, X}} -> X default 0
　　 may produce a runtime exceptions
　　 NullPointerException

3. element access

By -index element position in the array
　Array [I] [j]
　I position control of large arrays of small arrays
　j controlling the position of a small array elements

4. Loop poll

Enhanced for loop nested loop normal completion

The structure types are stored in the reference memory

Two-dimensional array structure stored in memory
　　int [] [] Array = new new int [3] [2];
　　// 3 each represent a 3-small array int []
　　// 2 represent each array has two small elements
　　// Array [0] [0] = 10;
　　// Array [0] [. 1] 2 = 0;

public class TestArray {
    public static void main(String [] args){
           int[][] array=new int[3][2];
           array[0][0]=10;
           array[0][3]=20;
           
           array[1]=array[0];
           array[0]=new int[4];
           array[0][0]=100;
           System.out.println(array[1][0]);  //10 

            //二维数组的动态初始化
           // int[][] array=new int[3][];//{{10,20},{0,0},{0,0}}                 
             //array[0]=new int[2];
             //array[0][0]=10;

             //array[0][4]=20;
             //array[0][2]=30;  //运行时异常 ArrayIndexOutOfBoundsException
            
            /*     
            //1.声明----初始化(静态)        
            int[][] array=new int[][]{{1,2},{3,4,5,6},{7,8,9}};
            //访问数组内的元素 ---index
            //int value= array[0][0]; //前面表示小数组位置 后面表示小数组中元素的位置
            //System.out.println(value);  // 1 array[2][3] 6    array[2][2] 9
            
            //数组的遍历/轮询
            for(int i=0;i<array.length;i++){ //遍历大数组中的小数组

                  for(int j=0;j<array[i].length;j++){  //遍历小数组中的元素
                       int value=array[i][j]; 
                       System.out.print(value+"\t"); 
                  }
                  System.out.println();
 
            }
            System.out.println("----------------");
        
            for(int[]arr: array){

               for(int value:arr){

                 System.out.println(value);
               }
             }*/

    }
}

Three-dimensional array

Create a good array stores a plurality of array int [] []
　　int [] [] [] = new new Array {{{1,2}, {3,4-}}, {{}, {}}, {{}, }}} {
　　 int [] [] [] array = new new int [. 3] [] [];
　　 each of which a three-dimensional array has a two dimensional array then there are two elements int

Two-dimensional array of exercises

1. Analog classmates weekly change position

{{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}}

import java.util.Scanner;
public class ChangeGroup {
     public static void main(String[] args){
        //创建一个二维数组 用来表示班级里的每一列同学
        int[][] array={{1,2,3,4},{5,6,7,8},{9,10,11,12},{13,14,15,16}};
        //设计每一周交换一次  几周?
        Scanner input =new Scanner(System.in);
        System.out.println("请输入一个周数,我来告诉您交换后的结果");
        int week=input.nextInt();  //6
         for(int i=1;i<week%4;i++){   
            int[] x=   array[0];
            array[0]=array[1];
            array[1]=array[2];
            array[2]=array[3];
            array[3]= x;
        }
        for(int[] arr:array) {
            for(int v: arr){
               System.out.print(v+"\t");
            }
               System.out.println();            
        }
    }

}