Java 中的數組

什麼是數組？

聲明一個數組

你如何聲明一個數組？

數據類型[] 數組名；

int[] myArray;

Object[] 
arrayOfObjects;  

數據類型 arrayName[];

int myArray[];

Object 
arrayOfObjects[];

創建數組

你如何創建一個數組？

new typeOfArray[length]; 

int[] myArray; // Array declaration
myArray = new int[10]; // Create (allocate memory for) an array of 10 ints

int[] myArray = new int [10]; // Declare the array and allocate memory "in one blow"

int[] myArray = new int[10];

Java 中的數組長度

int[] myArray = new int[10]; // Create an int array for 10 elements and name it myArray
System.out.println(myArray.length); // Display the array's length, i.e. the number of elements we can put into the array

10

初始化數組並訪問其元素

String[] seasons = new String[4]; /* Declare and create an array. Java allocates memory for an array of 4 strings, and each cell is set to null (since String is a reference type) */ 

seasons[0] = "Winter"; /* We set the first cell, i.e. the cell with index zero, to "Winter". Here we access the zeroth element of the array and write a specific value to it. */ 
seasons[1] = "Spring"; // We follow a similar procedure for the cell with index 1 (the second cell)
seasons[2] = "Summer"; // ... index 2
seasons[3] = "Autumn"; // and finally, index 3

String[] seasons = new String[] {"Winter", "Spring", "Summer", "Autumn"};

String[] seasons = {"Winter", "Spring", "Summer", "Autumn"};

Java 如何在屏幕上顯示一個數組？

String[] seasons = new String {"Winter", "Spring", "Summer", "Autumn"}; 
for (int i = 0; i < 4; i++) {
System.out.println(seasons[i]); 
}

Winter 
Spring 
Summer 
Autumn

Java中的一維和多維數組

Int[][] myTwoDimentionalArray = new int[8][8];

使用數組的有用方法

排序數組

在數組中搜索元素

將數組轉換為字符串

使用 sort、binarySearch 和 toString 的示例

class Main {
    public static void main(String[] args) {
        int[] array = {1, 5, 4, 3, 7}; // Declare and initialize the array
        System.out.println(array); // Try to display our array without using the toString method — the result is a hexadecimal number
        System.out.println(Arrays.toString(array)); // Display the array correctly 
        Arrays.sort(array, 0, 4); // Sort the entire array from the zeroth to the fourth element
        System.out.println(Arrays.toString(array)); // Display the sorted array
        int key = Arrays.binarySearch(array, 5); // Look for the number 5 in the sorted array. 
        // The binarySearch method will return the index of the array element we are searching for
        System.out.println(key); // Display the index of the number we searched for 
System.out.println(Arrays.binarySearch(array, 0)); // Now try to find a number that isn't in the array, 
        // and immediately display the result

    }
}

[I@1540e19d 
[1, 5, 4, 3, 7] 
[1, 3, 4, 5, 7] 
3 
-1

數組簡而言之

• 數組的基本特徵：放置在其中的數據類型、名稱和長度。
  最後一個屬性是在創建數組時確定的（當為數組分配內存時）。前兩個屬性是在聲明數組時確定的。

• 數組大小（單元格數）必須是int

• 數組創建後無法更改其長度。

• 可以通過其索引訪問數組元素。

• 數組中的元素，就像 Java 中的其他所有元素一樣，從零開始編號。

• 創建數組後，它會填充默認值。

• Java 中的數組與 C++ 中的數組不同。它們幾乎就像指向動態數組的指針。

關於數組的有用資料