1.數(shù)據(jù)類型

int，short，byte，long

double，float

char，String

2.變量

int var;
var = 12;
int var1 = 12;
final int v1 = 0;　//常量

C/C++變量的聲明和定義是分開的，JAVA不區(qū)分。

//c/c++
extern int a;    //聲明
int a = 0;        //定義

?3.運算符

JAVA的運算符、類型強制轉化與C相似。

?4.枚舉

enum Size {SMALL,MIDIUM,LARGE};

5.字符串

//定義
String e = "";
String greeting = "hello";//子串
String greeting = "hello";
String s = greeting.substring(0,3);//拼接
String expletive = "Expletive";
String pg = "deleted";
String msg = expletive + pg;
String msg1 =expletive + 1;
String all = String.join("/","S","M","L","XL");    //"S/M/L/XL"//不可修改
String str = "Help";
str = str.substring(0,3) + "p!";    //Help!//檢查字符串相等
s.equals(t);
"Help".equals(greeting);
"Hello".equalsIgnoreCase("help");//空串和null
if(str.length() == 0)if(str.equals(""))if(str == null)

6.構建字符串

StringBuilder builder = new StringBuilder();
builder.append(ch);        //append a charactor
builder.append(str);    //append a string

7.輸入輸出

import java.util.*;/*** This program demonstrates console input.* @version 1.10 2004-02-10* @author Cay Horstmann*/
public class InputTest
{public static void main(String[] args){Scanner in = new Scanner(System.in);// get first inputSystem.out.print("What is your name? ");String name = in.nextLine();// get second inputSystem.out.print("How old are you? ");int age = in.nextInt();// display output on consoleSystem.out.println("Hello, " + name + ". Next year, you'll be " + (age + 1));}
}

讀取密碼

Console cons = System.console();
String username = cons.readLine("User name:");
char[] passwd = cons.readPassword("Password:");

8.控制流程

控制流程與C相似

9.大數(shù)值計算

import java.math.*;
import java.util.*;/*** This program uses big numbers to compute the odds of winning the grand prize in a lottery.* @version 1.20 2004-02-10* @author Cay Horstmann*/
public class BigIntegerTest
{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.print("How many numbers do you need to draw? ");int k = in.nextInt();System.out.print("What is the highest number you can draw? ");int n = in.nextInt();/** compute binomial coefficient n*(n-1)*(n-2)*...*(n-k+1)/(1*2*3*...*k)*/BigInteger lotteryOdds = BigInteger.valueOf(1);for (int i = 1; i <= k; i++)lotteryOdds = lotteryOdds.multiply(BigInteger.valueOf(n - i + 1)).divide(BigInteger.valueOf(i));System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");}
}

10.數(shù)組

import java.util.*;/*** This program demonstrates array manipulation.* @version 1.20 2004-02-10* @author Cay Horstmann*/
public class LotteryDrawing
{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.print("How many numbers do you need to draw? ");int k = in.nextInt();System.out.print("What is the highest number you can draw? ");int n = in.nextInt();// fill an array with numbers 1 2 3 . . . nint[] numbers = new int[n];for (int i = 0; i < numbers.length; i++)numbers[i] = i + 1;// draw k numbers and put them into a second arrayint[] result = new int[k];for (int i = 0; i < result.length; i++){// make a random index between 0 and n - 1int r = (int) (Math.random() * n);// pick the element at the random locationresult[i] = numbers[r];// move the last element into the random locationnumbers[r] = numbers[n - 1];n--;}// print the sorted array
      Arrays.sort(result);System.out.println("Bet the following combination. It'll make you rich!");for (int r : result)System.out.println(r);}
}

注意：

Array.toSring()

Array.copyof()

Array.copyOfRange()

Array.sort()

Array.binarySearch()

Array.fill()

Array.equals()

11.類型

對象和對象變量

Data deadline;     //聲明一個變量，但是該變量沒有引用任何對象
deadline = new Data();    //初始化變量

自定義類

import java.time.*;/*** This program tests the Employee class.* @version 1.12 2015-05-08* @author Cay Horstmann*/
public class EmployeeTest
{public static void main(String[] args){// fill the staff array with three Employee objectsEmployee[] staff = new Employee[3];staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);// raise everyone's salary by 5%for (Employee e : staff)e.raiseSalary(5);// print out information about all Employee objectsfor (Employee e : staff)System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="+ e.getHireDay());}
}class Employee
{private String name;private double salary;private LocalDate hireDay;public Employee(String n, double s, int year, int month, int day){name = n;salary = s;hireDay = LocalDate.of(year, month, day);}public String getName(){return name;}public double getSalary(){return salary;}public LocalDate getHireDay(){return hireDay;}public void raiseSalary(double byPercent){double raise = salary * byPercent / 100;salary += raise;}
}

?

?

?

?

數(shù)學函數(shù)

Math，StrictMath

枚舉

enum{}

字符串String，null，不可修改，StringBuilder

char	charAt(int?index) Returns the?char?value at the specified index.
int	codePointAt(int?index) Returns the character (Unicode code point) at the specified index.
int	codePointBefore(int?index) Returns the character (Unicode code point) before the specified index.
int	codePointCount(int?beginIndex, int?endIndex) Returns the number of Unicode code points in the specified text range of this?String.
int	compareTo(String?anotherString) Compares two strings lexicographically.
int	compareToIgnoreCase(String?str) Compares two strings lexicographically, ignoring case differences.
String	concat(String?str) Concatenates the specified string to the end of this string.
boolean	contains(CharSequence?s) Returns true if and only if this string contains the specified sequence of char values.
boolean	contentEquals(CharSequence?cs) Compares this string to the specified?CharSequence.
boolean	contentEquals(StringBuffer?sb) Compares this string to the specified?StringBuffer.
static?String	copyValueOf(char[]?data) Equivalent to?valueOf(char[]).
static?String	copyValueOf(char[]?data, int?offset, int?count) Equivalent to?valueOf(char[], int, int).
boolean	endsWith(String?suffix) Tests if this string ends with the specified suffix.
boolean	equals(Object?anObject) Compares this string to the specified object.
boolean	equalsIgnoreCase(String?anotherString) Compares this?String?to another?String, ignoring case considerations.
static?String	format(Locale?l,?String?format,?Object...?args) Returns a formatted string using the specified locale, format string, and arguments.
static?String	format(String?format,?Object...?args) Returns a formatted string using the specified format string and arguments.
byte[]	getBytes() Encodes this?String?into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
byte[]	getBytes(Charset?charset) Encodes this?String?into a sequence of bytes using the given?charset, storing the result into a new byte array.
void	getBytes(int?srcBegin, int?srcEnd, byte[]?dst, int?dstBegin) Deprecated.? This method does not properly convert characters into bytes. As of JDK?1.1, the preferred way to do this is via the?getBytes()?method, which uses the platform's default charset.
byte[]	getBytes(String?charsetName) Encodes this?String?into a sequence of bytes using the named charset, storing the result into a new byte array.
void	getChars(int?srcBegin, int?srcEnd, char[]?dst, int?dstBegin) Copies characters from this string into the destination character array.
int	hashCode() Returns a hash code for this string.
int	indexOf(int?ch) Returns the index within this string of the first occurrence of the specified character.
int	indexOf(int?ch, int?fromIndex) Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
int	indexOf(String?str) Returns the index within this string of the first occurrence of the specified substring.
int	indexOf(String?str, int?fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
String	intern() Returns a canonical representation for the string object.
boolean	isEmpty() Returns?true?if, and only if,?length()?is?0.
static?String	join(CharSequence?delimiter,?CharSequence...?elements) Returns a new String composed of copies of the?CharSequence elements?joined together with a copy of the specified?delimiter.
static?String	join(CharSequence?delimiter,?Iterable<? extends?CharSequence>?elements) Returns a new?String?composed of copies of the?CharSequence elements?joined together with a copy of the specified?delimiter.
int	lastIndexOf(int?ch) Returns the index within this string of the last occurrence of the specified character.
int	lastIndexOf(int?ch, int?fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
int	lastIndexOf(String?str) Returns the index within this string of the last occurrence of the specified substring.
int	lastIndexOf(String?str, int?fromIndex) Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
int	length() Returns the length of this string.
boolean	matches(String?regex) Tells whether or not this string matches the given?regular expression.
int	offsetByCodePoints(int?index, int?codePointOffset) Returns the index within this?String?that is offset from the given?index?by?codePointOffset?code points.
boolean	regionMatches(boolean?ignoreCase, int?toffset,?String?other, int?ooffset, int?len) Tests if two string regions are equal.
boolean	regionMatches(int?toffset,?String?other, int?ooffset, int?len) Tests if two string regions are equal.
String	replace(char?oldChar, char?newChar) Returns a string resulting from replacing all occurrences of?oldChar?in this string with?newChar.
String	replace(CharSequence?target,?CharSequence?replacement) Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
String	replaceAll(String?regex,?String?replacement) Replaces each substring of this string that matches the given?regular expression?with the given replacement.
String	replaceFirst(String?regex,?String?replacement) Replaces the first substring of this string that matches the given?regular expression?with the given replacement.
String[]	split(String?regex) Splits this string around matches of the given?regular expression.
String[]	split(String?regex, int?limit) Splits this string around matches of the given?regular expression.
boolean	startsWith(String?prefix) Tests if this string starts with the specified prefix.
boolean	startsWith(String?prefix, int?toffset) Tests if the substring of this string beginning at the specified index starts with the specified prefix.
CharSequence	subSequence(int?beginIndex, int?endIndex) Returns a character sequence that is a subsequence of this sequence.
String	substring(int?beginIndex) Returns a string that is a substring of this string.
String	substring(int?beginIndex, int?endIndex) Returns a string that is a substring of this string.
char[]	toCharArray() Converts this string to a new character array.
String	toLowerCase() Converts all of the characters in this?String?to lower case using the rules of the default locale.
String	toLowerCase(Locale?locale) Converts all of the characters in this?String?to lower case using the rules of the given?Locale.
String	toString() This object (which is already a string!) is itself returned.
String	toUpperCase() Converts all of the characters in this?String?to upper case using the rules of the default locale.
String	toUpperCase(Locale?locale) Converts all of the characters in this?String?to upper case using the rules of the given?Locale.
String	trim() Returns a string whose value is this string, with any leading and trailing whitespace removed.
static?String	valueOf(boolean?b) Returns the string representation of the?boolean?argument.
static?String	valueOf(char?c) Returns the string representation of the?char?argument.
static?String	valueOf(char[]?data) Returns the string representation of the?char?array argument.
static?String	valueOf(char[]?data, int?offset, int?count) Returns the string representation of a specific subarray of the?char?array argument.
static?String	valueOf(double?d) Returns the string representation of the?double?argument.
static?String	valueOf(float?f) Returns the string representation of the?float?argument.
static?String	valueOf(int?i) Returns the string representation of the?int?argument.
static?String	valueOf(long?l) Returns the string representation of the?long?argument.
static?String	valueOf(Object?obj) Returns the string representation of the?Object?argument.

轉載于:https://www.cnblogs.com/TheImportanceOfLiving/p/7337221.html

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