Black Horse Programmer _ Common API Summary

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One. Object class:

1. Superclass of all reference data types (arrays, classes in class libraries, our custom classes)
2. Once our class inherits object, it has a method inherited from object:

Class object{

public int hashcode () {

function: Returns an int value as the key value of the hash table;
Default implementation: An int value generated based on the address of the object. Different objects, will return different values;
Later, our subclasses will rewrite.
}

Public final Class GetClass () {
Function: Gets the class object of this category
Default implementation: Get Class object
The final method cannot be overridden by a quilt class
}

Public String toString () {
Function: Returns the string representation of this object;
Default implementation: Class name + @ + Hex address (we're useless)
Rewrite: The property value of all members inside will be returned to a single string;
}

public boolean equals (Object obj) {
Function: Compare with parameter object is equal;
Default implementation: Compares the "address" with the argument for equality, and returns True if it is equal. (We're useless)
Rewrite: Compares all of our object's property values to the corresponding property values of the parameter and returns False if "All equals" returns true;
}

protected void Finalize () {
Function: This method is called before the garbage collector reclaims this object, and then the object space is removed;
Default implementation: None (Empty method)
Can be overridden as needed
}

Protected Object Clone () {
Function: Copy a copy of this object
Default implementation: Local method implementation
Rewrite as needed; Note: Classes that need to be assigned must implement the Cloneable interface
}

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Two. String class:

1. Represents a String object;
2. The "value" of a string object cannot be changed, but the reference can be changed;
3. Features: Can be directly assigned a "literal";
4. Typical interview questions:

String S1 = "abc";
String s2 = "abc"
String s3 = new String ("abc");
System.out.println (S1 = = s2);//true
System.out.println (S1 = = S3);//false
-----------------------------------------------------------
String S1 = "Hello";
String s2 = "World";
String s3 = "HelloWorld";
String S4 = "Hello" + "world";
String S5 = s1 + "World";
String s6 = "Hello" + s2;
String s7 = s1 + s2;
System.out.println (s3 = = S4);//true
System.out.println (s3 = = S5);//false
System.out.println (s3 = = S6);//false
System.out.println (s3 = = s7);//false

5. Construction Method:

public string (): instantiates an empty string; effect equivalent to: string s = "";
public string (byte[] bytes): Constructs a string using a byte[] array. (Converts a byte[] array to a string)
Public String (byte[] bytes,int offset,int length): Converts part of a byte[] array to a String
Public String (char[] value): Converts a char[] array to a String;
Public String (char[] value,int offset,int count): Converts part of a char[] array to a String
public string (string original): Constructs a new string using a string

6. Common methods:

1). Judging function:

Boolean equals (Object obj): Overrides object. Case-sensitive comparisons
Boolean equalsignorecase (String str): case-insensitive comparison
Boolean contains (String str): Determines whether STR is included in this string;
Boolean startsWith (String str): Whether to start with Str
Boolean endsWith (String str): Whether to end with Str
Boolean isEmpty (): Whether it is an empty string;

2). Get Features:

int length (): Distinguishes the length property of an array. Gets the lengths of the internal character sequences;
char charAt (int index): Returns the character of the index position;
int indexOf (int ch): Returns the index value of the character ch in the string, if not included, returns-1;
int indexOf (String str): Returns the index of the string str that appears in the string. If not included, returns-1;
int indexOf (int ch,int fromIndex): Find a character ch, starting from FromIndex;
int indexOf (String Str,int fromIndex): Finds a string str, starting from FromIndex;
int lastIndexOf (int ch): From the back forward, from right to left, but the returned index is from left to right, starting from 0;

string substring (int start): A string that intercepts the start of a punch starting to the end. Generates a new string with the original string unchanged;
String substring (int start,int end): From start, intercept to end-1 (not including end)

3). Conversion function:

Byte[] GetBytes (): Converts a string to a byte[] array;
Char[] ToCharArray (): Converts this string to char[] array;
Static String valueOf (char[] CHS): Static method. Converts a char[] array to a string
static String valueOf (int i): static method. Converts an int value to a string;
String toLowerCase (): Converts a character in a string to lowercase;
String toUpperCase (): converted to uppercase;
String concat (String str): Connects the argument string to the end of the current string. The effect is the same as the "+" operator;

4). Other functions:

1. Replacement function

String replace (char Old,char new): Replaces the characters in a string with the new character, replacing the original old character. Generates a new string, unchanged;

String Replace (String old,string New): Replaces the original old string with the new string;

2. Remove the string two spaces
String trim (): Does not contain spaces in;

3. Compare two strings in a dictionary order
int CompareTo (String str)
int comparetoignorecase (String str)

Three. Scanner class:
1.boolean hasnextxxx ():
2.nextXxx ();

Four. StringBuffer class:
Buffer pool class for 1.String.
The difference between 2.String and StringBuffer:
1). String: Its "value" is immutable;
2). StringBuffer: Its "value" is variable;
When we do the concatenation of strings many times, the use of string creates a lot of garbage space. It is recommended to use this class;
2. Construction Method:
Public StringBuffer (): Initial capacity 16
public stringbuffer (int capacity): initial capacity capacity
Public StringBuffer (String str): Constructs a stringbuffer using string.
3. Add Features:
Public StringBuffer append (String str): and various overloaded methods. Add any type of parameter to the end;
Public stringbuffer Insert (int offset,string str): Inserts a String into the offset position. The characters in the original position are shifted back in turn;
4. Delete function:
Public stringbuffer deletecharat (int index): Delete character at index position
Public StringBuffer Delete (int start,int end): Deletes all characters from start to end-1;
5. Replacement function:
Public stringbuffer replace (int start,int end,string str): Replaces all characters at start to end with Str;
6. Invert function:
Public StringBuffer reverse (): reverses internal strings;
7. Interception function:
public string substring (int start): Intercepts the return of a new string from start to end;
Public String substring (int start,int end): Intercepts all characters from start to end-1;

Differences between the StringBuffer class and the StringBuilder class:
1.StringBuffer is thread-safe and inefficient;
2.StringBuilder is thread unsafe; high efficiency;

Five. Arrays class:
1. The class of the array operation, there is no construction method, the internal contains a large number of static tool methods;
2. Common methods:
1). public static String toString (int[] a): Converts the int[] array to a String representation;
2). public static void sort (int[] a): Ascending sort int[] array;
3). public static int BinarySearch (int[] a,int key): Binary finds the key value in the int[] array;

Six. Wrapper class:
   basic data type   wrapper type
  byte   byte
  short     Short
  int      Integer
  long   Lon G
  char   Character
  float   float
  double&nbs p;  Double
  boolean    boolean

Seven, Integer class:
  1. The interior can contain an int value. It also contains some other methods for manipulating int values;
  2. Constructor:
   1). Integer (int value): Converts an int value to an integer;
   2). Integer (string s): Converts a String to an integer;
  3.int and String conversions:
   1). string--int:
    a.integer-->int parseint (string s)---int
     b.integer-->integer valueOf (String s)--intvalue ()--int
   2). INT----string:
    a.string-valueOf (int n)-and string
    b.integer -->string toString (int t)--String

4. Common methods:
   public int intvalue (): Returns an int value inside an integer
   public static int parseint (string s): Converts a string to int   
   public static string toString (int i) : Converts int to string
   public static Integer valueOf (int i): Converts int to Integer
    public static integer valueOf (string s): Converts a string to an integer
    basic binary conversion:
   public static string tobinarystring (int i):int--> binary-->string
   public static string tooctalstring (int i): int-to octal-to string
   public static string tohexstring (int i): INT-----hex--and S Tring
    Decimal to other binary:
   public static String toString (int i,int radix): The I value of a certain binary, Converted to a string representation. Radix: binary
    Other decimal:
   public static int parseint (String s,int Radix) : Converts a binary string representation of S to a decimal int value. Radix is the binary number;

Automatic packing and disassembly of 5.jdk5:
1. Auto-Boxing: Converts the "basic data type" to the corresponding "wrapper type";
Integer intobj = 10;
2. Automatic unpacking: The "package type" is converted to the corresponding "basic data type";
int n = intobj;

6. Common Interview Questions:

Integer V1 = 127;

Integer v2 = 127;

System.out.println (v1 = = v2);//true

Integer v3 = 128;

Integer v4 = 128;

System.out.println (v3 = = v4);//false

Integer v5 = 127;

Integer v6 = new Integer (127);

System.out.println (v5 = = V6);//false;

Eight. Character class:
1.char Packaging class;
2. Construction Method:
Character (Char v):
3. Common methods:
public static Boolean isuppercase (char ch): Determines whether it is a uppercase character
public static Boolean islowercase (char ch): Determines whether it is lowercase characters;
public static Boolean isdigit (char ch): Determines whether a number
public static char touppercase (char ch): Converts the character ch to uppercase;
public static char toLowerCase (char ch): Converts the character ch to lowercase;

-------<a href= "http://www.itheima.com" target= "blank" >android training </a> <a href= "/http/ Www.itheima.com "target=" blank ">java training </a>, look forward to communicating with you! ----------

Black Horse Programmer _ Common API Summary