Java array expansion instance code

In the process of writing a program, we often run out of array space, such as I have initialized an array int []a = {1,2,3,4,5,6,7,8,9,10}; I want to insert one element into the array subscript 3. What do I do? C language is too difficult to implement, you need to call memcpy function 1 to 1, but in java will not be so troublesome, there is a way called array expansion, easy to implement. Take a look at the code:

public class HelloWorld { 
  public static void main(String[] args){ 
  // Scanner s = new Scanner(System.in); 
  // System.out.println(" Please enter the 1 A digital "); 
  // int num = s.nextInt(); 
    // The index of this array can only go to 9 
    int []a = {1,2,3,4,5,6,7,8,9,10}; 
    // To increase  
    int []b = Getarray(a,3,100); 
    Demoe.PrintArray(b); 
     
  } 
  // Case: 1 An array has been initialized, and now its subscript 3 insert 1 An element 100 
  public static int[] Getarray(int []a , int index , int num){ 
    int src_array_length = a.length ;  
    int []b = new int[src_array_length+1] ; 
    for(int i = 0 ; i < a.length ; i++){ 
      b[i] = a[i] ;  
    } 
    a = b ; // If you still want to use it a, make a Point to the b 
    // And then from the end 1 The elements begin and end 1 The first of the elements 1 Copy the elements to the end 1 a  
    // And so on  
    for(int i = a.length - 1 ; i > index ; i--){ 
      a[i] = a[i-1]; 
    } 
    // Don't forget that the elements to be inserted are inserted into the corresponding array coordinates  
    a[index] = num ; 
    return a ; 
  } 
} 

This can also be done using the library functions in java

import java.util.Arrays; 
public class HelloWorld { 
  public static void main(String[] args){ 
  // Scanner s = new Scanner(System.in); 
  // System.out.println(" Please enter the 1 A digital "); 
  // int num = s.nextInt(); 
  int []a = {1,2,3,4,5}; 
  int []b = new int[a.length] ; 
    //1 The source array,  
    //2 , where to start the source array  
    //3 , target array  
    //4 , which location of the target array to start storing  
    //5 , make a few copies  
    //System.arraycopy(a, 0, b, 0, a.length); 
    //Demoe.PrintArray(b); 
    // capacity ---> A new 1 times  
    //a = Arrays.copyOf(a, 2*a.length) ; 
    //Demoe.PrintArray(a); 
    a = insertArray(a , 3 , 100) ; 
    // Print the array  
    System.out.println(Arrays.toString(a)); 
  } 
   
  // write 1 Function to any of the array of integers pos Position insert 1 An element value 
  public static int[] insertArray(int []a , int pos , int value){ 
    if(pos < 0 || pos > a.length + 1) // Returns the source array if the index subscript is incorrect   
      return a ; 
    // In the 1 Three elements, first expanded, then copied  
    a = Arrays.copyOf(a, a.length+1) ; 
    for(int i = a.length - 1 ; i > pos ; i--){ 
      a[i] = a[i-1] ; // After moving  
    } 
    a[pos] = value ; 
    return a ; 
  } 
} 

Operation results:

[1, 2, 3, 100, 4, 5]

conclusion

That's the end of this article on Java array extension example code, I hope to help you. If there is any deficiency, please let me know. Thank you for your support!