Java VS C++ 传值与函数参数传值

一、变量传值

Java

类对象 // 传引用  
原始数据类型 // 传值
String自身不带修改函数，每次操作都生成一个String对象。可以认为是传值。

 

C++

基本数据类型变量传值  //传值
一般指针传值  // 与int型相似，传值
类对象变量传值 // 相当于用某个对象来初使化新建对象
类指针对象变量传值  // 与int 类型相似，传值

二、函数传值

Java

拷贝复制传值

基本数据类型：拷贝复制变量的值，不能改变外部的地址和值。 类对象：拷贝复制传递对象的引用，不会改外部的地址，但能能过这个引用，改蛮对象的数据值。

C++

拷贝复制传值

基本数据类型：拷贝复制变量的值，不能改变外部的地址和值。 类对象：拷贝复制传值，在函数内部不能修改传入数据对象的数据。 指针或引用：能在函数内部修改传入对象或变量的数据。不能修改外部的地址，除非在函数内部有新建指针变量并将其返回给输入指针。如：int *set(int *p){return new int(10);}   int a = 11;int *pa = &a; pa = set(pa);。这一点JAVA中的引用也是如此。

Java 与 C++ 函数参数传值方式均为拷贝复制传值。两者区别只在于传入的东西的“表像”的不一样。

三、JAVA中的引用与C++的区别

JAVA中的引用，对类对象有此说法，对基础类型变量无此说法。

对类对象的引用，例如：设有类Test，则

Test t1 = new Test();

Test t2 = t1;

// t2为t1的一个引用（t1,t2具有相同的地址）

变量t1,t2相当于C/C++中的指针，它们指向同一个内存（具有相同的地址）

C++中，引用与指针是不同的概念。对对象及基础数据类型都有定义，设有类Test，如

Int a = 10;

Int &b = a;//创建a的一个引用。

Test ta = Test();

Test tb = ta;

Test &tc = ta;

// b 为a的一个引用，两者的地址相同。无论引用对象是类对象、数据类型对象还是指针。

 

 

顺便说一下

int a = 0;
int b = a;//先创建int型变量b中，在将a的值赋给b。

 

Test ta = Test();//创建Test 类对象ta

Test tb = ta;// 创建Test类对象，再用ta来初使化tb。故ta与tb的地址不同，数据相同

  // 此句与Testtb;tb = ta;等效

Test &tc = tb;// 创建类Test 对象tb的引用 tc。tc 与tb有相同的地址。指向同一片内存空间

 

Test *pa = new Test();// 创建类指针对象 pa，并默认初使化

Test *pb =pa; // 创建Test类指针对象并将 地址pa赋给pb。

Test *&pc = pa; // 创建 pa的一个引用pc ,从而pc与pa具有相同地址

// 故，pa，pb，pc指向同一内存空间
四、测试代码及运行结果

Java引用，函数传值代码

publicclass JavaCodeTest
{

public JavaCodeTest()

{
// TODO自动生成的构造函数存根

}

 

public static void main(String[] args)

{
// TODO自动生成的方法存根

Test a = new Test(001, "name001");

Test b = new Test(002, "name002");

print("a: " + a + " ");

a.print();

 

print("b: " + b + " ");

b.print();

print("Swapping......\n");

swap(a, b);

 

print("a: " + a + " ");

a.print();

 

print("b: " + b + " ");

b.print();

 

print("\n");

}

 

public static void swap(Test a, Test b)

{

Test tem = new Test();

tem.copy(a);

a.copy(b);

b.copy(tem);

 

}

 

public static void print(String str)

{

System.out.print(str);

}
}
 
classTest extends Object
{

int           id;

String        name;

 

Test()

{

}

 

Test(int id)

{

this.id = id;

}

 

Test(String name)

{

this.name = name;

}

 

Test(int id, String name)

{

this.id = id;

this.name = name;

}

 

Test(String name, int id)

{

this.id = id;

this.name = name;

}

 

public int getId()

{

return id;

}

 

public String getName()

{

return name;

}

 

public void print()

{

System.out.println("id = " + id + ",name = " +name);

}

 

public void copy(Test obj)

{

this.id = obj.id;

this.name = obj.name;

}

@Override

public Test clone()

{

return (new Test(this.id, this.name));

 

}
}
//输出结果

a:test.TestJava.Test@2a139a55 id = 1,name = name001
b:test.TestJava.Test@15db9742 id = 2,name = name002
Swapping......
a:test.TestJava.Test@2a139a55 id = 2,name = name002
b:test.TestJava.Test@15db9742 id = 1,name = name001

//引用测试
/*
 * C++/C引用测试
 */
#include<iostream>
usingnamespace std;
classTest
{
    public:

int val;

Test();

Test(int val);

~Test();
 

int getVal();

void setVal(int val);
};
Test::Test(){this->val= 0;};
Test::Test(intval){this->val = val;};
Test::~Test(){};
 
intTest::getVal(){return this->val;}
voidTest::setVal(int val){this->val = val;}
intmain()
{
    int a = 11;
    int b = a;
    int &c = a;
    cout << "Value:";
    cout << "a = "<< a<<"    b = "<< b<<"    c = "<< c<<endl;
    cout << "address:" <<"&a:" << &a <<"    &b" << &b<<"    &c" <<&c << endl;
 
    Test ta = Test(12);
    Test tb = ta;
    Test &tc = ta;
    Test td = Test();
    cout << endl <<"ObjectTest:" << endl;
    cout <<"Value:";
    cout << "ta.val = "<< ta.val << "    tb.val= "

    << tb.val <<"    tc.val = " << tc.val<< endl;
    cout << "Address:" <<&ta << "    "<< &tb << "   " << &tc << endl;
 
    cout << "Amendta"<<endl;
    ta.setVal(13);
    cout << "ta.val = "<< ta.val << "    tb.val= "

    << tb.val <<"    tc.val = " << tc.val<< endl;
    cout << "Address:" <<&ta << "    "<< &tb << "   " << &tc << endl;
    cout << "Amendtb"<<endl;
    tb.setVal(15);
    cout << "ta.val = "<< ta.val << "    tb.val= "

    << tb.val <<"    tc.val = " << tc.val<< endl;
    cout << "Address:" <<&ta << "    "<< &tb << "   " << &tc << endl;
    cout << "Amendtc"<<endl;
    tc.setVal(21);
    cout << "ta.val = "<< ta.val << "    tb.val= "

    << tb.val <<"    tc.val = " << tc.val<< endl;
    cout << "Address:" <<&ta << "    "<< &tb << "   " << &tc << endl;
 
    cout << "Init td with Address:" << &td << endl;
    td = ta;
    cout << "After td = ta ......tdget Address :  " << &td<< endl;
    cout << "The val in td :"<< td.val << endl;
 
    cout << endl <<"ObjectPointer Test:" << endl;
    Test *pa = new Test(11);
    Test *pb = pa;
    Test *&pc = pa;
    Test *pd = new Test();
    cout << "Value: " <<endl;
    cout << "pa : " <<pa->val << "\tpb : " << pb->val << "\tpc: " << pc->val << endl;
   cout << "Address : "<<endl << pa << "   " << pb << "   " << pc << "   " << endl;
    cout << "Amend pa :"<< endl;
    pa->setVal(14);
    cout << "pa : " <<pa->val << "\tpb : " << pb->val << "\tpc: " << pc->val << endl;
    cout << "Amend pb : "<< endl;
    pb->setVal(17);
    cout << "pa : " <<pa->val << "\tpb : " << pb->val << "\tpc: " << pc->val << endl;
    cout << "Amend pc；" << endl;
    pc->setVal(18);
    cout << "pa : " <<pa->val << "\tpb : " << pb->val << "\tpc: " << pc->val << endl;
    cout << "Init pd with Address :" << pd << endl;
    pd = pa;
    cout << "After : pd = pa......pdget Adress: " << pd << endl;
    cout << "The Value of pd :"<< pd->val << endl;
    return 0;
}

//输出结果

Value:a =11    b = 11    c = 11
address:&a:0x70fe04    &b0x70fe00    &c0x70fe04
 
ObjectTest:
Value:ta.val= 12    tb.val = 12    tc.val = 12
Address:0x70fdf0    0x70fde0   0x70fdf0
Amend ta
ta.val =13    tb.val = 12    tc.val = 13
Address:0x70fdf0    0x70fde0   0x70fdf0
Amend tb
ta.val =13    tb.val = 15    tc.val = 13
Address:0x70fdf0    0x70fde0   0x70fdf0
Amend tc
ta.val =21    tb.val = 15    tc.val = 21
Address:0x70fdf0    0x70fde0   0x70fdf0
Init tdwith Address :0x70fdd0
After td= ta ......td get Address :  0x70fdd0
The valin td :21
 
 
ObjectPointer Test:
Value:
pa :11        pb :11        pc : 11
Address :
0x1f14a0    0x1f14a0   0x1f14a0   
Amend pa:
pa :14        pb :14        pc : 14
Amend pb:
pa :17        pb :17        pc : 17
Amend pc；
pa :18        pb :18        pc : 18
Init pdwith Address : 0x1f14c0
After :pd = pa......pd get Adress: 0x1f14a0
The Valueof pd :18

//输出结果

Value:a =11    b = 11    c = 11
address:&a:0x70fe04    &b0x70fe00    &c0x70fe04
 
ObjectTest:
Value:ta.val= 12    tb.val = 12    tc.val = 12
Address:0x70fdf0    0x70fde0   0x70fdf0
Amend ta
ta.val =13    tb.val = 12    tc.val = 13
Address:0x70fdf0    0x70fde0   0x70fdf0
Amend tb
ta.val =13    tb.val = 15    tc.val = 13
Address:0x70fdf0    0x70fde0   0x70fdf0
Amend tc
ta.val =21    tb.val = 15    tc.val = 21
Address:0x70fdf0    0x70fde0   0x70fdf0
Init tdwith Address :0x70fdd0
After td= ta ......td get Address :  0x70fdd0
The valin td :21
 
 
ObjectPointer Test:
Value:
pa :11        pb :11        pc : 11
Address :
0x1f14a0    0x1f14a0   0x1f14a0   
Amend pa:
pa :14        pb :14        pc : 14
Amend pb:
pa :17        pb :17        pc : 17
Amend pc；
pa :18        pb :18        pc : 18
Init pdwith Address : 0x1f14c0
After :pd = pa......pd get Adress: 0x1f14a0
The Valueof pd :18

//返回指针
/*

 * return 地址

 */

#include <iostream>

using namespace std;

int *set(int *p)

{

    return new int(110);

}

int main()

{

    int a = 11;

    int *pa = &a;

    cout << "pa 的地址是：" << pa << endl;

    cout << "*pa = " << *pa << endl << endl;

    pa = set(pa);

    cout << " set ....." << endl;

    cout << "pa 的地址是：" << pa << endl;

    cout << "*pa = " << *pa << endl ;

    return 0;

}

// 输出结果
pa 的地址是：0x70fe34

*pa = 11

 set .....

pa 的地址是：0x7f14a0

*pa = 110