1. Array

An array is a container that stores a fixed number of data , And the container type is the same .

1.1 To define an array

Format 1 ：

 type [] Variable name ;

Format two ：

 type Variable name [];

There is no big difference between the two , But the scope of the latter definition has become wider , In addition to arrays, you can also define type variables , Examples are as follows ：

public class ArrayTest1 {
public static void main(String[] args) {
// Declared a a Array
int[] a;
// Declared a x Array and a y Variable
int x[], y;
}
}

1.2 Initialization of an array

Arrays cannot be used directly after definition , Space and elements are not allocated , At this time, you need to initialize the initial value to use . Initialization is divided into static 、 Move two .

1. dynamic initialization
   data type [] Variable name = new data type [ The length of the array ];

int[] x = new int[10];

2. initiate static
   data type [] Variable name = new data type []{ Elements 1, Elements 2,...};

data type [] Variable name = { Elements 1, Elements 2,...};

int y = {1, 2, 3};

Both static and dynamic initialization are OK .

Static and dynamic initialization can be one of them , Do not mix .

1.3 Array access

Now we define and initialize the array , Let's use . The use of arrays is to access data through indexes, also known as subscripts , The specific use is as follows ：
An array variable [ Indexes ]

int[] x = {1, 2, 3, 4};
int y = x[2];

When getting the contents of the array, you should pay attention to ：

• The initial index of the array is 0, The maximum subscript is length minus 1
• When accessing, the subscript must be within the subscript range of the array , Otherwise, an out of bounds exception will be thrown (ArrayIndexOutOfBoundsException)
• When the array is uninitialized （ namely x = null）, When accessing array elements , A null pointer exception will be thrown （NullPointerException）

1.4 Array application

Array is the unified management of a kind of data , There are many examples of this in life . For example, the math scores of the whole class , Floating point arrays can be used for unified management , Sort according to the requirements . During the interview , Data sorting is often asked , Then we will describe .

Here is a simple example , Print all grades ：

public class ArrayTest2 {
public static void main(String[] args) {
double[] x = {59.5, 60, 77, 145, 95};
for (int i = 0; i < x.length; i++) {
System.out.println(x[i]);
}
}
}

In the above example x.length Indicates the length of the obtained array , Usage for ( Array variable name .length)

This chapter ends , For personal learning and introduction to Xiaobai , Bosses do not spray ！

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