1, two-dimensional array introduction
【1 Overview:
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Is an array as an array of array elements, namely "array of arrays" on two-dimensional array essence,
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Type specifier array name [constant expression] [constant expressions].
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Also known as two-dimensional array matrix , ranks equal number matrix is called square. Symmetric matrix a [i] [j] = a [j] [i],
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Diagonal matrix: the outer square matrix of order n is zero main diagonal elements.
[2] format
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int [] [] arr = new int [3] [2]; the most used.
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Explanation
class Demo1_Array {
public static void main(String[] args) {
int[][] arr = new int[3][2];
/*
这是一个二维数组
这个二维数组中有3个一维数组
每个一维数组中有2个元素
[[I@19bb25a //二维数组的地址值
[I@da6bf4 //一维数组的地址值
0 //元素值
*/
System.out.println(arr); //二维数组
System.out.println(arr[0]); //二维数组中的第一个一维数组
System.out.println(arr[0][0]); //二维数组中的第一个一维数组的第一个元素
}
}
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int[][] arr = new int[3][];
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int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};
[3] Notes
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The following format may also represent two-dimensional array
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Data type array name [] [] = new data type [m] [n];
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Data Type [] array name [] = new data type [m] [n];
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Note the difference between defined below
int x; int number of a type of life is variable x
int y; int a data type, the variable y is ordered
int x,y;
int [] x; int defines a one-dimensional array of data types, designated as x
int [] y []; defines a two-dimensional array
int [] x, y []; x is a one-dimensional array, y is a two-dimensional array
2, illustrates a two-dimensional array
[Format 1]: int [] [] arr = new int [3] [2]; illustrated
class Demo2_Array {
public static void main(String[] args) {
int[][] arr = new int[3][2];
System.out.println(arr); //打印二维数组
System.out.println(arr[0]); //打印二维数组中的第一个一维数组
System.out.println(arr[0][0]); //打印二维数组中的第一个一维数组中的第一个元素
}
}
Two-dimensional array is the address of the value of a one-dimensional array, one-dimensional array to store the elements
[2] format: int [] [] arr = new int [3] [];
class Demo3_Array {
public static void main(String[] args) {
int[][] arr = new int[3][]; //这是一个二维数组,这个二维数组中有三个一维数组,三个一维数组都没有被赋值
System.out.println(arr[0]);
System.out.println(arr[1]);
System.out.println(arr[2]);
arr[0] = new int[3]; //第一个一维数组中可以存储三个int值
arr[1] = new int[5]; //第二个一维数组中可以存储五个int值
System.out.println("------------------");
System.out.println(arr[0]);
System.out.println(arr[1]);
System.out.println(arr[2]);
}
}-
Diagram
【3】int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};
class Demo4_Array {
public static void main(String[] args) {
int[][] arr = {{1,2,3},{4,5},{6,7,8,9}}; //这是一个二维数组,这个二维数组中每个大括号都代表一个一维数组
System.out.println(arr); //[[I@19bb25a,二维数组的地址值
System.out.println(arr[0]); //[I@da6bf4,一维数组的地址值
System.out.println(arr[0][0]); //1,一维数组中的元素值
}
}-
图解
