Article directory
1. Overview of arrays and static initialization
Introduction to Arrays
Array refers to a container that can be used to store multiple values of the same data type
- When an array container stores data, it needs to be considered in combination with implicit conversion
- Example: array container of int type (byte, short, int can be stored)
- Example: double type array container (byte, short, int, long, float, double can be stored)
array definition
The first:
data type [ ] array name
int [ ] array
The second type:
Data type array name[ ]
int array[ ]
Static initialization of arrays
- Initialization: It is the process of opening up space for the array container in memory and storing the data in the container
- Complete format: data type [] array name = new data type [] {element 1, element 2, element 3...};
- Simplified format: data type [] array name = {element 1, element 2, element 3...};
- Example: int[] array = {11,22,33};
- Example: double[] array2 = {11.1,22.2,33.3};
//定义学生年龄
int[] array = new int[]{
11, 22, 33};
int[] array1 ={
11, 22, 33}; //简写格式
//定义学生身高
double[] array2 = new double[]{
1.85, 1.86, 1.87};
double[] array3 = {
1.85, 1.86, 1.87};
//定义学生姓名
String[] array4 = new String[]{
"张三", "李四", "王五"};
String[] array5 = {
"张三", "李四", "王五"};
2. Array address value and element access
The address value of the array: indicates the location of the array in memory
int[] array1 ={
11, 22, 33}; //简写格式
System.out.println(array1);//地址值：[I@776ec8df
//[:表示当前是一个数组
//I:表示当前数组里面的元素都是int类型的
//@:表示一个间隔符号
//776ec8df:数组真正的地址值（十六进制）
element access
arrayName[index];
index:
- Index: also called subscript, corner mark.
- Features: start from 0, increase by +1 one by one, continuous and uninterrupted
public class array {
public static void main(String[] args) {
//利用索引对数组中的元素进行访问
int[] arr ={
1, 2, 3, 4, 5};
int number = arr[0];
System.out.println(number);
//把数据存储到数组中
arr[0] = 100;
//一但被覆盖后，原来的数据就不存在了
System.out.println(arr[0]);
}
}
Third, the traversal of the array
Use loops to quickly traverse arrays
In Java, regarding a length attribute of an array,
the calling method of length is: array name.length
public class array {
public static void main(String[] args) {
int[] array ={
1, 2, 3, 4, 5};
//利用循环取出元素
for(int i = 0; i < array.length; i++){
System.out.println(array[i]);
}
}
}
exercise 1
Define an array 1, 2, 3, 4, 5, and sum
public class array {
public static void main(String[] args) {
int[] arr = {
1,2,3,4,5};
//定义求和变量
int count = 0;
for (int i = 0; i < arr.length; i++) {
//i是数组中的索引
//arr[i]是数组中的元素
count = count + arr[i];
}
System.out.println(count);
}
}
exercise 2
Define an array 1 to 10, and count how many numbers are divisible by 3
public class array {
public static void main(String[] args) {
int[] arr = {
1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
//定义统计变量
int count = 0;
for (int i = 0; i < arr.length; i++) {
if(arr[i] % 3 == 0){
count++;
}
}
System.out.println(count);
}
}
Exercise 3
Modify the elements in the array during traversal.
Define an array of 1-10.
If it is an even number, it will be half of the current number. If it is an odd number, it will be doubled.
public class array {
public static void main(String[] args) {
int[] arr ={
1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
for (int i = 0; i < arr.length; i++) {
if(arr[i] % 2 == 0){
arr[i] = arr[i] / 2;
}else{
arr[i] = arr[i] * 2;
}
}
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
}
}
Fourth, the dynamic initialization of the array
Dynamic initialization: only the length of the array is specified during initialization, and the system assigns the initial value to the array
- Format: data type [] array name = new data type [array length];
- Example: int[] arr = new int[3];
define a dynamically initialized array and assign
public class array {
public static void main(String[] args) {
//假如新生有50人来报道，暂时不知道姓名，所以定义一个动态数组
String[] arr = new String[50];
//进行赋值
arr[0] = "张三";
arr[1] = "李四";
System.out.println(arr[0]);//张三
System.out.println(arr[1]);//李四
System.out.println(arr[2]);//null-动态初始化值
}
}
The law of the default initialization value of the array
- Integer type: default initialization value 0
- Decimal type: default initialization value 0.0
- Character type: default initialization value '/u0000' space
- Boolean type: the default initialization value is false
- Reference data type: default initialization value null
Difference between static initialization and dynamic initialization
Dynamic initialization: manually specify the length of the array, and the default initialization value is given by the system
- Only the number of elements is specified, but the specific value is not specified. It is recommended to use dynamic initialization
Static initialization: Manually specify the array elements, and the system will calculate the length of the array based on the number of elements
- The specific data to be operated has been specified in the requirements, and the static initialization can be done directly