Today's tip is about java of Arrays class （ Tool class for array operation ） Learning of .
first , Let's first understand Arrays What is a class , about Arrays class ：
Arrays Class in java.util In the package , It mainly includes various methods of manipulating arrays
Guide package when using :
import java.util.Arrays
secondly , Learn what methods this class has and how to use them ：
Arrays Class contains various methods for manipulating arrays （ Such as sorting and searching ）.
This class also contains a static factory , You can think of arrays as lists .“ Static factory ” explain Arrays Class contains many static methods , So that programmers can easily call .（ Referring to the invocation of static methods , We can use it as an example method
object . Method name Make a call （ Not recommended ）; Can also be used Class name . Method name Make a call （ recommendation ）.）
Here are some Arrays Common methods of classes ：
1.Arrays.toString（ Array name a）
public static String toString( type [] a) // Remember to change the type to the corresponding data type when using
Method function ： Returns a string representation of the contents of a specified array . The string representation consists of a list of array elements , Enclosed in square brackets （ "[]" ） in . Adjacent elements are composed of characters ", "
（ Comma followed by a space ） Separate . Element is converted to a string by String.valueOf(short). return "null" If a yes null.
Why use this method ? Not directly ：
System.out.println(a); //a Is an array name
First of all, this is definitely not possible , Because the output is an array a Address of ;
Of course, we can also use for Loop method outputs the elements in the array one by one , Although this is feasible , But if we just want to see what elements are in the array , There's no need to do this , use Arrays.toString（ Array name ）
You can directly output the contents of the array .
Test code ：
import java.util.Arrays; public class Dem1 { public static void main(String[]
args) { int[] a= {1,4,3,2}; System.out.println(a);
System.out.println(Arrays.toString(a)); } }
Running results ：
[Ljava.lang.Integer;@5ca881b5 [1, 4, 3, 2]
2.Arrays.sort（ Group name a）
public static void sort( type [] a)
Default ascending sort of array .
Implementation considerations ： The sorting algorithm is Vladimir Yaroslavskiy,Jon Bentley and Joshua Bloch Two axis quick sort provided .
The algorithm is available on many datasets O（n log（n）） performance , Cause other quicksort to degrade to secondary performance , And usually more than traditional （ Uniaxial ）Quicksort Achieve faster .
For us, Xiaobai is undoubtedly using for Loop statements , It can be said that I have a headache , therefore Arrays Class sort（） The method is undoubtedly beneficial to Xiaobai .
Here is the code test ：
import java.util.Arrays; public class Dem1 { public static void main(String[]
args){ int[] a= {1,4,3,2}; System.out.println(Arrays.toString(a)); // Contents of array before sorting
Arrays.sort(a); System.out.println(Arrays.toString(a)); // Contents of sorted array } }
Running results ：
[1, 4, 3, 2] // Before sorting [1, 2, 3, 4] // After sorting
3.Arrays.equals（ Array name 1, Array name 2）
public static boolean equals( type [] a, type [] a2)
If two specified arrays are equal to each other , Then return true .
If both arrays contain the same number of elements , The two arrays are considered equal , And all corresponding element pairs in the two arrays are equal .
in other words , If two arrays contain the same elements in the same order , Then they are equal . in addition , If both array references are null, Then they are considered equal .
take care ： The two arrays being compared must be of the same type !!!
Test code ：
import java.util.Arrays; public class Dem1 { public static void main(String[]
args){ int[] arr1= {1,4,3,2}; // Original array int[] arr2= {1,6,5,7}; // Same number of array elements , Different elements
int[] arr3= {1,4,3,2,5}; // The front elements of the array are the same , Different number int[] arr4= {1,4,3,2}; // Array elements and number are the same
double[] dou= {1,4,3,2}; // Array elements and number are the same , But the array type is different
System.out.println(Arrays.equals(arr1, arr2));
System.out.println(Arrays.equals(arr1, arr3));
System.out.println(Arrays.equals(arr1, arr4)); //
System.out.println(Arrays.equals(arr1, dou)); Error reporting } }
Running results ：
false // Same number of array elements , Different elements false // The front elements of the array are the same , Different number true // Array elements and number are the same
Error reporting information ：
Exception in thread "main" java.lang.Error: Unresolved compilation issues ： type Arrays Methods in
equals（int[], int[]） For parameters （int[], double[]） Not applicable Syntax error , take “VariableDeclarators” Insert to full
LocalVariableDeclaration in Syntax error , take “;” Insert to full LocalVariableDeclarationStatement in
Cannot resolve Error reporting
That's all for today's knowledge sharing , Thank you for reading !（ Xiaobai records learning , Please give me more advice ; The method and introduction of this article are based on jdk1.8
API Help documents find , If something is wrong, it may be a translation problem , Or maybe it was the wrong hand （ dog's head ）. Then help the document , You can search online , Many resources , If you can't find it, you can confide in me .）
Technology
Daily Recommendation