1. Java Language Foundation (array overview and Definition Format description)
2. Java Language Foundation (initialization of arrays initialized dynamically)
- A: What is the initialization of an array
- is to open up contiguous memory space for arrays and assign values to each array element
- B: How to initialize an array
- A: Dynamic initialization only specifies the length, the system gives the initialization value
- B: Static initialization gives the initialization value, the system determines the length of the
- C: Dynamic initialization format:
- data type [] Array name = new data type [array length];
- D: Case Demo
- Output array names and arrays elements
3. Java Language Foundation (memory allocation in Java and differences between stacks and heaps)
- A: Stack (Master)
- B: Heap (Master)
- Storing new arrays or objects
- C: Method Area
- Object-oriented section explanation
- D: Local Method area
- E: Register
4. Java Language Foundation (array of memory plots 11 arrays)
5. Java Language Foundation (array of memory plots 22 arrays)
6. Java Language Foundation (array of memory plots 33 references two arrays)
- A: Drawing Demo
- Three references, two array references to the same address
7, Java Language Foundation (initialization of the array static initialization and memory diagram)
- A: The Static initialization format:
- Format: data type [] Array name = new data type []{element 1, element 2,...};
- Simplified format:
- data type [] Array name = {element 1, element 2,...};
- B: Case Demo
- Explanation of the logarithm group
- Output array names and arrays elements
- C: Drawing Demo
8. Java Language Basics (two common minor problems with array operations out of bounds and null pointers)
- A: Case Demo
- A:arrayindexoutofboundsexception: Array index out-of-bounds exception
- Reason: You have accessed an index that does not exist.
- B:nullpointerexception: null pointer exception
- Cause: The array is no longer pointing to heap memory. You also use the array name to access the element.
- Int[] arr = {A-i};
- arr = null;
- System.out.println (Arr[0]);
9, the Java Language Foundation (array operation 1 times calendar)
10, the Java Language Foundation (array of Operations 2 get the most value)
A: Case Demo
Array gets the maximum value (gets the minimum value in the array)
public static int getMax(int[] arr) { int max = arr[0]; for (int i = 1;i < arr.length ;i++ ) { //从数组的第二个元素开始遍历 if (max < arr[i]) { //如果max记录的值小于的数组中的元素 max = arr[i]; //max记录住较大的 } } return max;}
11. Java Language Foundation (operation of Array 3 inversion)
A: Case Demo
array element inversion (that is, swapping elements)
public static void reverseArray(int[] arr) { for (int i = 0;i < arr.length / 2 ; i++) { //arr[0]和arr[arr.length-1-0]交换 //arr[1]和arr[arr.length-1-1]交换 //arr[2]和arr[arr.lentth-1-2] //... int temp = arr[i]; arr[i] = arr[arr.length-1-i]; arr[arr.length-1-i] = temp; }}
12, the Java Language Foundation (array of Operations 4 look up the table method)
A: Case Demo
Array Lookup Table method (according to the keyboard input index, find the corresponding week)
public static char getWeek(int week) { char[] arr = {‘ ‘,‘一‘,‘二‘,‘三‘,‘四‘,‘五‘,‘六‘,‘日‘}; //定义了一张星期表 return arr[week]; //通过索引获取表中的元素}
13, the Java Language Foundation (array of Operations 5 basic lookup)
A: Case Demo
Array element Lookup (finds the index of the first occurrence of the specified element in the array)
public static int getIndex(int[] arr,int value) { for (int i = 0;i < arr.length ;i++ ) { //数组的遍历 if (arr[i] == value) { //如果数组中的元素与查找的元素匹配 return i; } }
14, the Java Language Foundation (two-dimensional array overview and Format 1 explanation)
- A: A Two-dimensional array overview
- B: two-dimensional array format 1
- int[][] arr = new int[3][2];
- C: Interpretation of the two-dimensional array format 1
D: Precautions
- E: Case Demo
- Define two-dimensional arrays, output two-dimensional array names, one-dimensional array names, one element
15, Java Language Foundation (two-dimensional array format 1 memory plot)
- A: Drawing Demo
- Drawing explains the problem of the above two-dimensional array name, one-dimensional array name, and the value of an element
16, Java Language Foundation (two-dimensional array format 2 explanation and memory plot)
- A: Two-dimensional array format 2
- int[][] arr = new int[3][];
- B: Interpretation of the two-dimensional array format 2
- C: Case Demo
- Explain formats, output data, and draw memory graphs
17, Java Language Foundation (two-dimensional array format 3 explanation and memory plot)
- A: Two-dimensional array format 3
- Int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};
- B: Interpretation of the two-dimensional array format 3
- C: Case Demo
- Explain formats, output data, and draw memory graphs
18, Java Language Foundation (two-dimensional array exercises 1 times calendar)
A: Case Demo
Requirements: two-dimensional array traversal
The outer loop controls the length of the two-dimensional array, which is actually the number of one-dimensional arrays.
The inner loop controls the length of a one-dimensional array.
int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};for (int i = 0;i < arr.length ;i++ ) { //获取到每个二维数组中的一维数组 for (int j = 0;j < arr[i].length ;j++ ) { //获取每个一维数组中的元素 System.out.print(arr[i][j] + " "); } System.out.println();}
19. Java Language Basics (two-dimensional array exercises 2 summation)
- A: Case Demo
需求:公司年销售额求和某公司按照季度和月份统计的数据如下:单位(万元)第一季度:22,66,44第二季度:77,33,88第三季度:25,45,65第四季度:11,66,99int[][] arr = {{22,66,44},{77,33,88},{25,45,65},{11,66,99}};int sum = 0; //定义变量,记录每次相加的结果for (int i = 0;i < arr.length ;i++ ) { //获取每一个一维数组 for (int j = 0;j < arr[i].length ;j++ ) { //获取每一个一维数组中的元素 sum = sum + arr[i][j]; //累加 }}System.out.println(sum);
20, the Java Language Foundation (study questions Java in the parameter transfer problem and diagram)
- A: Case Demo
看程序写结果,并画内存图解释public static void main(String[] args) { int a = 10; int b = 20; System.out.println("a:"+a+",b:"+b); change(a,b); System.out.println("a:"+a+",b:"+b); int[] arr = {1,2,3,4,5}; change(arr); System.out.println(arr[1]);}public static void change(int a,int b) { System.out.println("a:"+a+",b:"+b); a = b; b = a + b; System.out.println("a:"+a+",b:"+b);}public static void change(int[] arr) { for(int x=0; x<arr.length; x++) { if(arr[x]%2==0) { arr[x]*=2; } }}
Java EE Basics (v)