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1. What is a two-dimensional array

An array in which multiple elements are one-dimensional arrays in a two-dimensional array is called a two-dimensional array.

two。 Define format

Format 1:

Data type of element [] [] name of array = data type of new element [length of two-dimensional array] [length of one-dimensional array]

Int [] [] a = new int [3] [2]

Explanation: there are also three one-dimensional arrays in this two-dimensional array, each with two elements.

Format 2:

Data type of element [] [] name of array = data type of new element [length of two-dimensional array] []

Int [] [] a = new int [3] []

Explanation: there are also three one-dimensional arrays in this two-dimensional array, and the number of elements in each one-dimensional array is uncertain.

Format 3:

The data type of the element [] [] array name = {{element 1, element 2, … }, {element 1, element 2, … }, }

Int [] [] a = {{1rec 2jue 3}, {4je 5}, {5pr 6pr 7je 8}}

Explanation: there are three one-dimensional arrays in this two-dimensional array, and the number of elements in each one-dimensional array is different.

The first one-dimensional array contains three elements.

The second one-dimensional array contains two elements.

The third one-dimensional array contains four elements.

3. The use of two-dimensional arrays package shuzu;public class erwei {public static void main (String [] args) {int [] [] a = new int [3] []; System.out.println (a); / [[I@7852e922, the address of the output array a / / because each array is not initialized, the three arrays are null. System.out.println (a [0]); / / null System.out.println (a [1]); / / null System.out.println (a [2]); / / null int [] aqum1 = {1pm 2pm 3}; / / define an one-dimensional array of a1. A [0] = aql; / / assign the value of the array aqum1 to the first one-dimensional array of array a. Int [] aqum2 = {4pm 5}; / / defines an one-dimensional array of a2. A [1] = aq2; / / assign the value of the array aqum2 to the second one-dimensional array of array a. Int [] aqum3 = {6 I@70dea4e 7, 8, 9}; a [2] = axi3; System.out.println (a [0]); / / [I@4e25154f, output the address of the first one-dimensional array System.out.println (a [1]); / / [I@70dea4e, output the address of the second one-dimensional array System.out.println (a [2]) / / [I@5c647e05, output the address of the third one-dimensional array / / the following program is the element of the output array: System.out.println (a [0] [0]); / / 1 outputs the first element of the first array, System.out.println (a [0] [1]) / / 2 outputs the second element of the first array System.out.println (a [0] [2]); / 3 outputs the third element of the first array System.out.println (a [1] [0]); / 4 similarly outputs the first element of the second array System.out.println (a [1] [1]) / / 5 System.out.println (a [2] [0]); / 6 similarly outputs the first element of the third array, System.out.println (a [2] [1]); / 7 System.out.println (a [2] [2]); / 8 System.out.println (a [2] [3]) / / 9}} 4. Traversal of two-dimensional array

The for each loop statement cannot automatically process every element in a two-dimensional array because it processes rows, and each one-dimensional array is a row, so two nested loops are used to loop each element of the two-dimensional array, as shown below:

Example 1:

/ / use the format: for (double [] row: a) for (double value: row) do something with value// example: double [] [] arr = {{1 row 2 5 row 4}, {4 2 row 7}, {3 row 6 row 9 4}}; how many elements are there in the for (double [] row: arr) / / cycle, which refers to an one-dimensional array. {how many elements are there in the for (double b: row) / / loop, where elements refer to the elements in each one-dimensional array. System.out.print (b + "); / / prints out the elements of each array. System.out.println (); / / Line break}

/ / output result:

1.0 2.0 5.0 4.0

4.0 2.0 5.0 7.0

3.0 6.0 9.0 4.0

Example 2:

Int [] [] a = {{1Power2, 3}, {4, 5}, {5, 6, 7, 7, 8}}; for (int I = 0; I < a. Resume; iDiffect +) / / this structure principle is roughly the same as the above, except that there are restrictions on the subscript of the element. {for (int j = 0; j < a [I] .length; jacks +) / / elements of the loop I array. System.out.print (a [I] [j] + "); / / outputs the j element of the I array. System.out.println (); / / line wrapping. }

/ / output result:

1 2 3

4 5

5 6 7 8

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