First, the definition of an array
/** * One-dimensional array definition * * Insert elements into an array * / Public void Case1 () { // declare int [] of arr1; // declare initialized + int [] = arr2 is new new int [. 3 ]; // array assigned arr2 is [0] =. 1 ; arr2[1] = 2; arr2[2] = 3; // declare + static initialization, arr3 and arr4 as int [] = ARR3 new new int [] {. 1, 2,. 3,. 4,. 5 }; int [] = {arr4. 1, 2,. 3,. 4,. 5 }; }
Second, iterate
/** * One-dimensional array of access & traversal */ public void case2() { int[] arr = new int[]{1, 2, 3, 4, 5}; // 普通for循环 for (int i = 0; i < arr.length; i++) { System.out.println(arr[i]); } // the foreach, enhanced for loop for ( int NUM: ARR) { System.out.println(num); } // third way, jdk1.8 support that way Arrays.stream (arr) .forEach (System.out :: println); }
Third, the two-dimensional array
/** * Define two-dimensional array, initialization, access, traversal */ public void case3() { // declare int [] [] arr1; // declare initialized + int [] [] = arr2 is new new int [. 3] [2 ]; arr2[0][0] = 1; arr2[0][1] = 1; // declare + static initialization,. 3. 3 * int [] [] = {{ARR3. 1, 2,. 3}, {. 4,. 5,. 6}, {. 7,. 8,. 9 }}; } /** * Traverse the two-dimensional array * / Public void case4 () { int[][] arr = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; // 第一种方式 for (int i = 0; i < arr.length; i++) { for (int j = 0; j < arr[i].length; j++) { System.out.println(arr[i][j]); } } // second way for ( int [] INTS: ARR) { for ( int I: INTS) { System.out.println(i); } } }
IV Summary
definition
- A plurality of data types by pressing the same order together to form the structure
Attributes
- Name: Address stored in the memory array
- Index: each element has a unique position in the array for positioning element
- Element: each of the data array, i.e. the elements
- Length: the number of elements in the array i.e.
Feature
- Ordered the elements
- Continuous memory space
- Belonging to the reference data types
note
- Once the specified length can not be modified i.e.
Fifth, practice
1, the definition of an array of integers, find the largest element
/** * Array Exercise: define an array of integers, find the largest element */ public void case1(){ int[] arr = new int[10]; for (int i=0;i<10;i++){ arr[i] = i; } System.out.println(Arrays.toString(arr)); int max = arr[0]; for (int j=0;j<arr.length;j++){ if (arr[j] > max){ max = arr[j]; } } System.out.println(max); }
2, the definition of a two-dimensional array, and find all the elements
/** * Array Exercise: Defining a two-dimensional array, plus all the elements required and * / Public void Case2 () { // declare and initialize a two-dimensional array int [] [] = ARR new new int [. 5] [. 3 ]; // generates a two-dimensional array for ( int I = 0; I <. 5 ; I ++ ) { for ( int J = 0; J <. 3; J ++ ) { arr[i][j] = i + j; System.out.print(arr[i][j]+" "); } } // Each loop element two-dimensional array and then summed int SUM = 0 ; for ( int I = 0; I <arr.length; I ++ ) { for ( int J = 0; J <ARR [I] .length; ++ J ) { sum += arr[i][j]; } } // wrap System.out.println (); System.out.println(sum); }
3, to the array location specified insertion / deletion of an element
/** * To insert a specified position array element */ int[] insertarray(int[] arr, int index, int value){ int[] newArr = new int[arr.length + 1]; for (int i = 0; i < arr.length; i++) { newArr[i] = arr[i]; } for (int i = newArr.length - 1; i > index; i--) { newArr[i] = newArr[i - 1]; } newArr[index] = value; arr = newArr; return arr; } /** * Delete the array element at the specified position */ int[] deletearray(int[] arr, int index){ int[] newArr = new int[arr.length - 1]; for (int i = 0; i <= arr.length - 1; i++){ if (i < index){ newArr[i] = arr[i]; } else if (i > index){ newArr[i-1] = arr[i]; } } return newArr; }