Example Analysis of Java object-oriented Array
This article mainly introduces the example analysis of Java object-oriented array, which is very detailed and has certain reference value. Friends who are interested must finish it!
An array of Java face objects
1. One-dimensional array
1. Description of the array: a combination of the same type of data.
Description: the ① array is a reference data type, and the elements of the array can be basic data types or reference data types.
two。 Declaration and initialization of one-dimensional array
① dynamic initialization: array declaration and initialization are performed separately
Int [] numbers = new int [5]
② static initialization: array declaration and initialization occur at the same time
Int [] numbers = new int [] {1pm 2pm 3pm 4}
Int [] numbers = {1pm 2pm 3pm 4}
Note: the length of the array is immutable once the array is created, either dynamically or statically.
3. Reference to one-dimensional array elements: subscript (index value)-subscript is the length from 0 to the array-1
Int [] numbers = new int [2]
Numbers [0] = 1; / / assignment
System.out.println (numbers [0]); / / get the value of the element
4. Properties of the array: length- represents the length of the array
Int [] numbers = new int [2]
Int l = numbers.length
5. Traversal of one-dimensional array
Int [] numbers = new int [2]
For (int I = 0; I < numbers.length; iTunes +) {
System.out.println (numbers [I])
}
6. Default initialization values for one-dimensional array elements: the same as the default values for basic and reference data types.
7. Memory structure of one-dimensional array
Painted by ps:Excel, average level, make do with it.
two。 Two-dimensional array
1. How to understand two-dimensional array? The elements in a two-dimensional array are one-dimensional arrays. (elements in an array or an array)
Description: elements of a two-dimensional array are reference data types
two。 Declaration and initialization of two-dimensional array
/ / dynamic initialization
String [] [] persons = new String [2] [3]
String [] persons = new String [2] []
Persons [0] = new String [2]
Persons [1] = new String [5]
/ / static initialization
String [] [] persons = new String [] [] {{"a", "110"}, {" b "," 120"}}
String [] [] persons = {{"a", "110"}, {" b "," 120th "}}
3. How to reference a two-dimensional array element: get the element at a location in the array by using the subscript
String [] [] persons = {{"a", "110"}, {" b "," 120th "}}
System.out.println (persons [0] [0])
4. Property of 2D array: length
String [] [] persons = {{"a", "110"}, {" b "," 120th "}}
Length of persons.length; / / two-dimensional array
Persons [0] .length; / / the length of the element at position 0 in the two-dimensional array
5. Traverse two-dimensional array elements:
String [] [] persons = {{"a", "110"}, {" b "," 120th "}}
For (int I = 0; I < persons.length; iTunes +) {
For (int j = 0; j < persons [I] .length; jacks +) {
System.out.println (persons [I] [j])
}
}
6. Default initialization values for two-dimensional array elements:
The default value for the elements of the ① 2D array is null
The default values and basic data types of the elements of the ② two-dimensional array are the same as the reference data types.
7. Memory structure of two-dimensional array
3.Arrays utility class
Because under the lang package, there is no need for the guide package to call the
Int [] numbers = {12pm 38pm 1je 2je 3je 4je 5je 6}
Int [] numbers2 = {12pm 38pm 1je 2je 3je 4je 5}
/ / determine whether two arrays are equal (the value and number of elements)
Boolean equals = Arrays.equals (numbers, numbers2)
System.out.println (equals)
/ / toString (): outputs the elements in the array
String str = Arrays.toString (numbers)
System.out.println (str)
/ / fill (int [] njinint val): change the value of the array element to val
Arrays.fill (numbers, 100)
Str = Arrays.toString (numbers)
System.out.println (str)
/ / sort (int [] numbers)
Arrays.sort (numbers2)
System.out.println (Arrays.toString (numbers2))
/ / dichotomy search: premises must be sorted. If you can't find a return-1
Int index = Arrays.binarySearch (numbers2, 1)
System.out.println (index)
4. Common anomalies
Int [] numbers = new int [2]
/ *
*
* ArrayIndexOutOfBoundsException
, /
/ / numbers [2] = 5; the subscript is out of bounds
/ / numbers [- 1] = 10
/ / int [] [] n = new int [2] []
/ / n [2] = new int [10]
/ *
* NullPointerException
, /
String [] str = {"aa", "bb"}
/ / String string = str [0] .toUpperCase ()
/ / System.out.println (string)
Str = new String [2]
/ / System.out.println (str [0] .toString ())
5. Deformable parameter
* deformed parameters:
*
* format: public void add (int... Numbers {}
*
* description:
* 1. Deformable parameters of the same type and arrays of the same type are not overloaded (the type is the same as the number)
* 2. Deformable parameters can only be placed on the last one in the formal parameter list.
* 3. There can be only one deformable parameter in a method
* 4. The number of deformable parameters can be 0 or 1 or more
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