Introduction to the differences between Java sets and arrays and examples of mutual conversion

Differences between arrays and Collections:

(1) Arrays are fixed in size, and the same array can only store data of the same type (basic type / reference type)

(2) Java collections can store and manipulate a variable number of sets of data. (3) If the program does not know how many objects are needed and needs to automatically expand the capacity when the space is insufficient, the container class library needs to be used, and array is not applicable.

Contact: use the corresponding toArray () and arrays The aslist () method can recall the transformation.

The difference between list and ArrayList

1. List is an interface, and the list feature is order, which ensures that elements are saved in a certain order

ArrayList is its implementation class, which is a list implemented by array

Map is an interface. The map feature is to find objects according to an object

HashMap is its implementation class. The map implemented by HashMap with hash table is to use the hashcode of the object (hashcode () is the method of the object) for fast hash search (for hash lookup, see < < data structure > >)

2. Generally, if it is not necessary, the recommended code only deals with list and map interfaces

For example: listlist = newarraylist();

The reason for this is that list is a generic implementation. If you want to change the type of list, you only need to:

Listlist=newLinkedList();// LinkedList is also the implementation class of list and the brother class of ArrayList

In this way, there is no need to modify other code, which is the elegance of interface programming

Another example is the following declaration in the method of the class:

privatevoiddoMyAction(Listlist){}

In this way, this method can handle all classes that implement the list interface and implement generic functions to a certain extent

3. If you feel that the performance of ArrayList and HashMap cannot meet your needs during development, you can customize your custom class by implementing list, map (or collection)

List, method of converting set to array

There are two forms of toArray function, one without parameters and the other with parameters. Note that the size of the array should be specified in the form with parameters.

Program code:

Conversely, the array is converted to list, set.

Note: this cannot be done directly for int [] arrays, because the parameter of the aslist () method must be an object. You should first convert int [] to integer []. The same is true for other primitive arrays, which must first be converted to the corresponding wrapper type array.

summary

The above is all about the difference between Java sets and arrays and the examples of mutual conversion in this paper. I hope it will be helpful to you. Interested friends can continue to refer to this website:

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