An array is a container that holds multiple elements (an array is a collection of data). An array can hold both primitive and reference data types. Data is stored in a heap. The "memory address" of a Java object is stored. One-dimensional, 2 d, 3 d, multidimensional arrays (mainly using one dimensional and two dimensional array) 8, all array object has length attribute, used to retrieve the number of array elements in 9, the type of elements in the array is unified, int array can store type int 10, array elements stored memory address is continuous to permutation (regular), Array is a simple data structure. The memory address of the first element in an array is the memory address of the entire array object. Retrieval efficiency high 1) elements of the memory address is continuous 2) because of the same element type, so take up the space is the same size (3) know the first element of memory address, know the element of space size, know the subscript elements, can be directly calculated by a mathematical expression a subscript elements on the memory address, through the memory address location elements Disadvantages: 1) The efficiency of adding and deleting elements is low, because the memory address of the elements in the array is continuous, which will cause the elements to move forward or backward uniformly. 2) It cannot store a large amount of data, so it is difficult to find a large contiguous memory space.  int[] array1; double[] array2; boolean[] array3; Object[] array4; Int [] array = {100,200,300,55}; int[] array = {100,200,300,55}; Int [] array = new int[5]; // Initializes an array of 5 lengths of type int, each element defaults to 0 A two-dimensional array is a special one-dimensional array in which each element is a one-dimensional array. A three-dimensional array is a special two-dimensional array in which each element is a one-dimensional array.  int[][] array = {{1, 1, 1}, {2, 3, 4, 5}, {0, 0, 0}}; Dynamically initialize 2d arrays: int[][] array = new int[3][4]; Array [subscript of a one-dimensional array in a two-dimensional array][subscript of the elements in the one-dimensional array]Copy the code