前言
C++ 作為 C語言的延伸,而Java 被設(shè)計成 C++ 簡化的繼任者,他們都有著很多共同點,如基本類型相同:int、char、float、long、double,當(dāng)然也有一些不同,如Java char 是 2個字節(jié),一個字節(jié)8位,如:0000 1111,那么2個字節(jié)就是16位,而C++里的char只有8位,也就是1個字節(jié),這個要注意。它們還都有表示true、false的數(shù)據(jù)類型,且if ... else,while,for和switch都是相同的,為了更快的能從Java轉(zhuǎn)到C++,我準(zhǔn)備了這篇文章,希望對你也有幫助。
打印
Java
System.out.print("Hello World!");
System.out.println("Hello World!");
C++
//第一種實現(xiàn)
std::cout << "Hello World!";
std::cout << "Hello World!" << std::endl;
//第二種,如果使用命名空間就不需要再std::
#include <iostream>
using namespace std;
int main() {
cout << "Hello World!";
cout << "Hello World!" << endl;
return 0;
}
常量
Java
final int x = 2;
final int y = 1;
C++
//使用 #define 預(yù)處理器。
#define X 2
#define Y 1
//使用 const 關(guān)鍵字。
const int X = 2;
const int Y = 1;
變量
Java
int w;
int z = 2;
z = 3;
w = 1;
C++
int w;
int z = 2;
z = 3;
w = 1;
賦值為空
Java
String lastName;
lastName = null
C++
string lastName;
lastName = NULL; // 編譯器報錯,無法賦值,想要釋放調(diào)用 lastName.clear();函數(shù)
判空
Java
if(text != null){
int length = text.length();
}
C++
string text;
//C++ 字符串無需判空,返回長度0
cout << text.length() << endl;
字符拼接
Java
String name = "John";
String lastName = "Smith";
String text = "My name is: " + name + " " + lastName;
C++
string name = "John";
string lastName = "Smith";
string text = "My name is: " + name + " " + lastName;
換行字符
Java
String text = "First Line\n" +
"Second Line\n" +
"Third Line";
C++
string text = "First Line\nSecond Line\nThird Line";
三元運(yùn)算
Java
String text = x > 5 ? "x > 5" : "x <= 5";
C++
string text = x > 5 ? "x > 5" : "x <= 5";
位操作
Java
int andResult = a & b;
int orResult = a | b;
int xorResult = a ^ b;
int rightShift = a >> 2;
int leftShift = a << 2;
C++
int andResult = a & b;
int orResult = a | b;
int xorResult = a ^ b;
int rightShift = a >> 2;
int leftShift = a << 2;
父子關(guān)系
Java
if(x instanceof Integer){ }
C++
(is_base_of<Integer, x>::value ? "true" : "false")
類型轉(zhuǎn)換
Java
double a = 1.9;
int b = (int) a;
int d = a; //報錯
String c = String.valueOf(b);
C++
double a = 1.9;
int b = (int)a;
int d = a; //隱士轉(zhuǎn)換
string c = to_string(b); //字符串轉(zhuǎn)換
Switch
Java
int a = 1;
String b;
switch (a) {
case 0:
case 1:
b = "1";
break;
case 2:
b = "2";
break;
default:
b = "default";
break;
}
C++
int a = 1;
String b;
switch (a) {
case 0:
case 1:
b = "1";
break;
case 2:
b = "2";
break;
default:
b = "default";
break;
}
For循環(huán)
Java
for (int i = 1; i < 11 ; i++) { }
for (int i = 1; i < 11 ; i+=2) { }
for (String item : collection) { }
C++
for (int i = 1; i < 11 ; i++) { }
for (int i = 1; i < 11 ; i+=2) { }
for (string &item : collection) { }
//或 auto 類型也是 C++11 新標(biāo)準(zhǔn)中的,用來自動獲取變量的類型
for (auto &item : collection) { }
集合
Java
final List<Integer> numbers = Arrays.asList(1, 2, 3);
C++
int numbers[5] = {1, 2, 3};
Map
Java
final Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "One");
map.put(2, "Two");
map.put(3, "Three");
C++
map < int , string > map;
map.insert(pair < int,string > (1,"One"));
map.insert(pair < int,string > (1,"Two"));
map.insert(pair < int,string > (1,"Three"));
簡單總結(jié)下
我們回顧一下,這次對C++基本類型、位運(yùn)算、類型判斷、操作符,集合等做了簡單的對比,其實不難發(fā)現(xiàn),C++真的和Java很像,總體感覺C++書寫稍復(fù)雜一些,也有比Java寫起來簡單的部分等,有更多的新奇等著你去發(fā)現(xiàn),下期接著研究,拜。