The best Java arrays Tutorial In 2024, In this tutorial you can learn Declare an array variable,Creating an array,Working with arrays,foreach loop,Array as a function of the parameters,Array as the return value of a function,Arrays class,
One array for each programming language for data structures are important, of course, different languages and the realization process of the array are not the same.
Java language provides an array is used to store a fixed size elements of the same type.
You can declare an array of variables, such as the numbers [100] instead of direct statements 100 independent variables number0, number1, /en/en, number99.
This tutorial will introduce declare Java array creation and initialization, and gives the corresponding code.
You must first declare an array variable, you can use the array in your program. Here is the syntax for declaring an array variable:
dataType[] arrayRefVar; // 首选的方法 或 dataType arrayRefVar[]; // 效果相同,但不是首选方法
Note: We recommend using dataType [] arrayRefVar style statement declare an array variable. dataType arrayRefVar [] style derived from C / C ++ language, Java is used to make C / C ++ programmers can quickly understand the java language.
Here is the code example both syntax:
double[] myList; // 首选的方法 或 double myList[]; // 效果相同,但不是首选方法
Java language using the new operator to create an array, the syntax is as follows:
arrayRefVar = new dataType[arraySize];
The above syntax statements do two things:
Declare an array variable, the array can be used to create and complete a statement as follows:
dataType[] arrayRefVar = new dataType[arraySize];
In addition, you can create an array using the following method.
dataType[] arrayRefVar = {value0, value1, /en., valuek};
Elements of the array is accessed through an index. The array index starts from 0, so the index value from 0 to arrayRefVar.length-1.
First, the following statement declares an array variable myList, then created a 10 element contains an array of type double, and its reference assigned to myList variable.
public class TestArray { public static void main(String[] args) { // 数组大小 int size = 10; // 定义数组 double[] myList = new double[size]; myList[0] = 5.6; myList[1] = 4.5; myList[2] = 3.3; myList[3] = 13.2; myList[4] = 4.0; myList[5] = 34.33; myList[6] = 34.0; myList[7] = 45.45; myList[8] = 99.993; myList[9] = 11123; // 计算所有元素的总和 double total = 0; for (int i = 0; i < size; i++) { total += myList[i]; } System.out.println("总和为: " + total); } }
The above example output is:
总和为: 11367.373
The following image depicts an array myList. Here myList has 10 double array element, its index from 0-9.
Size and type of the array elements of the array is determined, so when processing array elements, we usually use the basic loop or foreach loop.
This example shows how to create a complete, initialize and manipulate arrays:
public class TestArray { public static void main(String[] args) { double[] myList = {1.9, 2.9, 3.4, 3.5}; // 打印所有数组元素 for (int i = 0; i < myList.length; i++) { System.out.println(myList[i] + " "); } // 计算所有元素的总和 double total = 0; for (int i = 0; i < myList.length; i++) { total += myList[i]; } System.out.println("Total is " + total); // 查找最大元素 double max = myList[0]; for (int i = 1; i < myList.length; i++) { if (myList[i] > max) max = myList[i]; } System.out.println("Max is " + max); } }
The above examples compiled results are as follows:
1.9 2.9 3.4 3.5 Total is 11.7 Max is 3.5
JDK 1.5 introduced a new type of loop, called the foreach loop or enhanced circulation, it is not used under circumstances through the array subscript.
This example is used to display all the elements in the array myList:
public class TestArray { public static void main(String[] args) { double[] myList = {1.9, 2.9, 3.4, 3.5}; // 打印所有数组元素 for (double element: myList) { System.out.println(element); } } }
The above examples compiled results are as follows:
1.9 2.9 3.4 3.5
Arrays can be passed as a parameter to the method. For example, the following example is a method int array elements in printing.
public static void printArray(int[] array) { for (int i = 0; i < array.length; i++) { System.out.print(array[i] + " "); } }
The following example calls printArray method to print out the 3,1,2,6,4 and 2:
printArray(new int[]{3, 1, 2, 6, 4, 2});
public static int[] reverse(int[] list) { int[] result = new int[list.length]; for (int i = 0, j = result.length - 1; i < list.length; i++, j--) { result[j] = list[i]; } return result; }
Examples of the above result in an array as the return value of the function.
java.util.Arrays class can easily manipulate arrays, it provides all the methods are static. It has the following features:
Specific instructions please see the following table:
No. | Method and Description |
---|---|
1 | public static int binarySearch (Object [] a, Object key) Binary search algorithm using an object in a given array search for a given value (Byte, Int, double, etc.). Array must be sorted before calling. If the lookup value is contained in an array, the index of the search key returns; otherwise, (- (insertion point) - 1). |
2 | public static boolean equals (long [] a, long [] a2) If the two specified arrays of long equal to one another, it returns true. If both arrays contain the same number of elements, and two arrays of all corresponding pairs of elements are equal, the two arrays are considered equal. In other words, if the two arrays in the same order that contains the same elements in the two arrays are equal. The same applies to all other basic data types (Byte, short, Int, etc.). |
3 | public static void fill (int [] a, int val) Int value Assigns the specified int array of the specified range of each element. The same applies to all other basic data types (Byte, short, Int, etc.). |
4 | public static void sort (Object [] a) The specified array of objects into ascending order according to the natural ordering of its elements. The same applies to all other basic data types (Byte, short, Int, etc.). |