ArrayList collection basic usage

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Collection Overview

aggregate , Containers of variable length

1 ArrayList Set variable length principle ：

• ArrayList aggregate ： So is the underlying principle , Array ; The initial size length is 10

1 Initializes a length of 10 Array of , The values are stored in sequence , When the storage space of the array is not enough, enter the second link ;
2 Create an original array length 1.5 A new array of multiples , Copy the contents of the original array to the new array , Then the data not saved in the first link , Save to new array ;
Be careful ： Selection of sets and arrays 【 The length remains unchanged, using an array , Set with variable length 】

2 ArrayList aggregate

• ArrayList Tectonics 1
  • public ArrayList();
• Generic ：<>
  • Add... After the class name <>, Can make the data type stored in the collection , Make type restrictions ;
  • Only reference data types can be used in angle brackets , Cannot be a basic data type

Solution ：【 Basic types have corresponding wrapper classes 】

Basic data type	Corresponding packaging
int	Integer
short	Short
byte	Byte
double	Double
float	Float
char	Character

3 ArrayList Common member methods

• increase
  • public boolean add(E e); Add data to the tail of the collection , Return the status of successful addition
  • public void add(int index,E element); Queue jumping and adding

 ArrayList<String> list1 = new ArrayList<>();// establish list aggregate 
        list1.add(" Zhang San ");                    // Additive elements 

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• Delete
  • public E remove(int index); Delete the elements in the collection according to the index
  • public boolean remove( Elements ); Delete the contents of the collection according to the elements , Duplicate elements delete only the first ; Return the status of successful addition

 ArrayList<String> list1 = new ArrayList<>();// establish list aggregate 
        list1.add(" Zhang San ");                    // Additive elements 
        list1.add(" Wang Wu ");
        list1.add(" Shangguan iron egg ");
        list1.add(" Zhang San ");
        list1.add(" Zhuge order ");
        list1.remove(" Zhang San ");                // Delete according to the element 
        list1.remove(2);                    // Delete the element according to the index value 

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• Change
  • public E set(int index,E element); Modify the specified index location , Returns the overwritten element

ArrayList<String> list1 = new ArrayList<>();// establish list aggregate 
        list1.add(" Zhang San ");                   // Additive elements 
        list1.add(" Wang Wu ");
        list1.add(" Shangguan iron egg ");
        list1.add(" Zhang San ");
        list1.add(" Zhuge order ");  
        list1.set(2," Yearly salary one million ");             // Modify set data 

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• check
  • public E get(int index); Index based , Get the elements in the collection

      ArrayList<String> list1 = new ArrayList<>();// Create set 
        list1.add(" Zhang San ");                        // Additive elements 
        list1.add(" Wang Wu ");
        list1.add(" Shangguan iron egg ");
        list1.add(" Zhang San ");
        list1.add(" Zhuge order ");
        list1.get(2);                           // Find set elements 

4 ArrayList Set basic cases

4.1 Case study 1

Create a collection of stored strings , Storage 5 String elements , find 4 One word name , And print

 public static void main(String[] args) {
    
        ArrayList<String> list1 = new ArrayList<>();// establish list aggregate 
        list1.add(" Zhang San ");                           // Additive elements 
        list1.add(" Wang Wu ");
        list1.add(" Shangguan iron egg ");
        list1.add(" Zhang San ");
        list1.add(" Zhuge order ");
        for (int i = 0; i < list1.size(); i++) {
        // Ergodic set 
            String name = list1.get(i);             // Get collection elements 
            if (list1.get(i).length()==4){
              // Determine if the string length is 4
                System.out.println(name);           // Print 4 The name of a word 
            }
        }
    }

Conclusion

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