Chapter 2 Summary

数组（一维数组为例）

1：数组的创建
JAVAThe type of the array in can be a primitive data type,也可以是引用类型.
[数据类型]数组名[];
[数据类型][]数组名;

import java.util.Arrays;
public class MainClass {
    
    public static void main(String[] args) {
    
       int[] intArray = {
    0,1,2,3};//指定数组长度为3,分配内存.
       char charArray[] = new char[]{
    '好','好','学','习'};//使用new初始化数组,Then assign values ​​to the contents of the array.
       String stringArrya[] = new String[4];//指定数组长度为4,分配内存,没有内容.
        for (int a:intArray) {
    
            System.out.println(a);
        }
        for (char c:charArray) {
    
            System.out.println(c);
        }
        for (String s:stringArrya) {
    
            System.out.println(s);
        }
    }
}

0
1
2
3
好
好
学
习
null
null
null
null

2：Array traversal and output
1).foreach遍历:
循环访问数组中的每个元素.

import java.util.Arrays;
public class MainClass {
    
    public static void main(String[] args) {
    
       int[] intArray = {
    0,1,2,3};//指定数组长度为3,分配内存.
        for (int a:intArray) {
    
            System.out.println(a);
        }
    }
}

0
1
2
3

2).简单的for循环遍历.

3).Arrays类中的toString静态方法:

public class MainClass {
    
    public static void main(String[] args) {
    
       int[] intArray = {
    0,1,2,3};//指定数组长度为3,分配内存.
        System.out.println(Arrays.toString(intArray));
    }
}

[0, 1, 2, 3]

对于多维数组,toString()methods cannot be used directly,需要deepToString()A static method is required to output all elements in a multidimensional array:
toString()The method returns the memory address where the array of each dimension is stored.
deepToString()The method returns the contents of each dimension of a multidimensional array

import java.util.Arrays;
public class MainClass {
    
    public static void main(String[] args) {
    
       int intArray[][] = new int[2][2];//指定数组长度为3,分配内存.
        intArray[0] = new int[]{
    0,1};
        System.out.println(Arrays.toString(intArray));
        System.out.println(Arrays.deepToString(intArray));
    }
}

[[I@1540e19d, [I@677327b6]
[[0, 1], [0, 0]]

3.length();取数组长度.

4.增
1):通过for循环遍历数组,Assign a value to each element in the array.
2):ArraysThe class provides static methods that can batch add elements to an arrayfill();The input parameters are the array of elements to be added and the value to be added;It is also possible to specify the range of indices into which the array is to be added（左闭右开区间）,The input parameters are the start index and end index：

import java.util.Arrays;
public class MainClass {
    
    public static void main(String[] args) {
    
       String[] string = new String[4];
       char[] char_one = new char[4];
       Arrays.fill(string,1,3,"学");
       Arrays.fill(char_one,'学');
        System.out.println(Arrays.toString(string));
        System.out.println(Arrays.toString(char_one));
    }
}

[null, 学, 学, null]
[学, 学, 学, 学]

5.删
The array length cannot be modified,But we can refer to the method of adding an element,Rebuilds an array with elements removed,In order to achieve the purpose of deleting the specified element.

import java.util.Arrays;
public class MainClass {
    
    private static char[] DeleteArray(char[] array,int index){
    
        char[] newArray = new char[array.length-1];
        for(int i = 0;i < newArray.length;i++){
    
            if(i < index){
    
                newArray[i] = array[i];
            }else{
    
                newArray[i] = array[i+1];
            }
        }
        return newArray;
    }
    public static void main(String[] args) {
    
       char[] charArray = new char[]{
    '好','好','学','学','习'};
        System.out.println(Arrays.toString(charArray));
        charArray = DeleteArray(charArray,2);
        System.out.println(Arrays.toString(charArray));
    }
}

[好, 好, 学, 学, 习]
[好, 好, 学, 习]

6.查
Arrays类中提供了binarySearch()方法,Can find the position of an element in an array,Return if not found-1;

public static void main(String[] args) {
    
       char[] charArray = new char[]{
    '好','好','学','习'};
       int index = Arrays.binarySearch(charArray,'学');
        System.out.println(index);
    }

2

7.比较
Arrays类中提供equals()方法,用来比较两个数组的内容是否相同.

public static void main(String[] args) {
    
       char[] charArray_1 = new char[]{
    'a','b','c','d'};
       char[] charArray_2 = new char[]{
    'a','b','c','d'};
       char[] charArray_3 = new char[]{
    'a','c','d'};
       boolean bool = Arrays.equals(charArray_1,charArray_2);
       System.out.println(bool);
       bool = Arrays.equals(charArray_1,charArray_3);
        System.out.println(bool);
    }

true
false

8.数组复制
Arrays类中提供了数组复制的方法copyOf();

 public static void main(String[] args) {
    
       char[] charArray_1 = new char[]{
    'a','b','c','d'};
       char[] charArray_2 = Arrays.copyOf(charArray_1,4);
       System.out.println(Arrays.toString(charArray_2));

    }

[a, b, c, d]