Array, String,stringbuilder, collection

1. Definition of arrays, traversal, and methods

Definition: int arr[] = {1,2,3,4,5};// static initialization
int arr1[]= New int[5];//dynamic initialization
To iterate over an array:

for (int i = 0; i < arr.length; i++) {System.out.println (arr[i]);}

The methods and properties of the

array :length length;

2
Definition:
//mode 1
//string (string original): Encapsulates string data into a String object
String s1 = new String ("Hello");
Mode 2
//string (char[] value): Encapsulates the data of a character array into a string object
char[] chs = {' h ', ' e ', ' l ', ' l ', ' o '};
String s2 = new string (CHS);
//Mode 3
//string (char[] value, int index, int count): Encapsulates part of the data in a character array into a string object
//string s3 = new String (chs,0, Chs.length length);
String s3 = new String (chs,1,3);
//Mode 4
string s4 = "Hello";

Traversal:
//gets the length of the string using the length () method
for (intx=0; x<s.length (); x + +) {
System.out.println (S.charat (x));
}
Method:
Judging function method

? Boolean equals (Object obj): Compares the contents of a string? Boolean Equalsignorecase (String str): Compares the contents of a string for the same, ignoring case? Boolean StartsWith (String str): Determines whether the string object begins with the specified str? boolean endsWith (String str): Determines whether the string object ends with the specified str

? Get functional methods

? int Length (): Gets the length of the string, in fact, the number of characters? Char charAt (int index): Gets the character at the specified index? int indexOf (String str): Gets the index of the first occurrence of STR in a string object. No return-1? string substring (int start): Intercepts a string from start to end of string? string substring (int start,int end): Intercepts the string from start to end, including start, excluding end

? Conversion Function method

? char[] ToCharArray (): Converts a string to a character array? String toLowerCase (): Converts a string to a lowercase string? String toUpperCase (): Converts a string to an uppercase string

? remove whitespace and split function methods

? char[] ToCharArray (): Converts a string to a character array? String toLowerCase (): Converts a string to a lowercase string? String toUpperCase (): Converts a string to an uppercase string

　　

3.definition, traversal, and method of StringBuilder
Defined:
Creating objects
StringBuilder builder = new StringBuilder ();
//method of calling append directly

Builder.append ("Hello"); Builder.append ("World"); Builder.append (true); Builder.append (100);

Chained programming

Builder.append ("Hello"). Append ("World"). Append (True). Append (100); System.out.println ("Builder:" +builder);

　　

Traversal://Fangfali Creates a StringBuilder type inversion and then ToString becomes a string type
Publicstatic string Myreverse (string s) {
String--StringBuilder--reverse ()--string
string s = new string ("Hello");//Defining a string string
StringBuilder builder= New StringBuilder (s);//change string string to StringBuilder object
Builder.reverse ();//Call Reverse Inversion method
string result = Builder.tostring ();//Turn StringBuilder object into string string
Return result;
}

Method:
Add Features
Public StringBuilder Append (any type): Adds data and returns its own object
such as: Builder.append (TRUE);
? reversal function
? public StringBuilder Reverse ()
such as: Builder.reverse ();

The string turns into StringBuilder:

StringBuilder constructs a method, or a Append method such as: string s = new string ("Hello");//defines a string string StringBuilder builder= new StringBuilder (s);//change string string to StringBuilder object or: StringBuilder builder = new StringBuilder (s);

　　StringBuilder turns into a string:

The method of the StringBuilder class public string toString () such as: string result = Builder.tostring ();

4. definition, traversal, and method of the collection

Defined:
To create a collection object
Arraylist<string>list = new arraylist<string> ();

Traverse:

3. Iterate through the collection, fill the left side of the element with a length of less than 4 with string 8, and in the console print the output modify all elements in the collection for (int i = 0; i < list.size (); i++) {if (List.get (i). Length () <4) {L Ist.set (i, 8 + list.get (i));}} SYSTEM.OUT.PRINTLN (list);

Method:
? Add elements
? public boolean Add (E): add element
such as: List.add ("Hello");
public void Add (int index,e Element): Adds an element at the specified index
such as: List.add (1, "Android");
? Get elements
? Public E get (int index): Returns the element at the specified index
? Set length
public int size (): Returns the number of elements in the collection
? Delete an Element
? public boolean remove (Object O): Deletes the specified element, returning whether the deletion succeeded
Public E Remove (int index): Deletes the element at the specified index and returns the deleted element
? modifying elements
? public E Set (int index,e element): Modifies the element at the specified index, returning the modified element

Array, String,stringbuilder, collection