JAVA之等号、传类对象参数与c++的区别

在JAVA中用等号对类对象进行赋值，实际上操作的是对象的地址。

eg：

package MyText;

class ClassA
{
	int value;
	public void seta(int value)
	{
		this.value = value;
	}
	public void show()
	{
		System.out.println("the value:" + value);
	}
}
public class MyText {
	public static void main (String []args)
	{
		ClassA a = new ClassA();
		a.seta(1);
		a.show();
		System.out.println("a:" + a);//a的地址
		ClassA b = new ClassA();
		b.seta(2);
		b.show();
		System.out.println("b:" + b);//b的地址
		System.out.println("======================");
		b = a;
		a.show();
		b.show();
		System.out.println("a:" + a + ", b:" + b);
		b.seta(3);
		a.show();
		b.show();
		System.out.println("a:" + a + ", b:" + b);
	}
}

运行结果：

the value:1
a:MyText.ClassA@14a55f2
the value:2
b:MyText.ClassA@15093f1
======================
the value:1
the value:1
a:MyText.ClassA@14a55f2, b:MyText.ClassA@14a55f2
the value:3
the value:3
a:MyText.ClassA@14a55f2, b:MyText.ClassA@14a55f2

在java中向函数传入类对象参数实际上操作的也是地址

eg：

package MyText;

class ClassA
{
	int value;
	public void seta(int value)
	{
		this.value = value;
	}
	public void show()
	{
		System.out.println("the value:" + value);
	}
}
public class MyText {
	public static void showClassA(ClassA a)
	{
		a.show();
		System.out.println("a:" + a);
		a.seta(5);
		a.show();
		System.out.println("a:" + a);
	}
	public static void main (String []args)
	{
		ClassA a = new ClassA();
		a.seta(1);
		a.show();
		System.out.println("a:" + a);
		showClassA(a);
		a.show();
		System.out.println("a:" + a);
	}
}

运行结果：

the value:1
a:MyText.ClassA@5e55ab
the value:1
a:MyText.ClassA@5e55ab
the value:5
a:MyText.ClassA@5e55ab
the value:5
a:MyText.ClassA@5e55ab
而在C++中向函数传递类对象参数时，是按值传递的，即实参与形参间进行成员变量赋值操作，而不是地址

eg：

# include <iostream>
using namespace std;

class ClassA
{
private:
    int value;
public:
    void seta(int value)
    {
        this->value = value;
    }
    void show()
    {
        cout<<"the value : "<<value<<endl;
    }
};
void show(ClassA a)
{
    a.show();
    cout<<"a:"<<&a<<endl;
    a.seta(5);
    a.show();
}
int main ()
{
    ClassA a;
    a.seta(3);
    a.show();
    cout<<"a:"<<&a<<endl;
    show(a);
    a.show();
}

运行结果：

the value : 3
a:0x22fefc
the value : 3
a:0x22fea0
the value : 5
the value : 3

Process returned 0 (0x0)   execution time : 0.130 s
Press any key to continue.
对于利用等号对对象进行赋值，实际上也是对对象成员的值按值传递，而不是传递地址

eg：

# include <iostream>
using namespace std;

class ClassA
{
private:
    int value;
public:
    void seta(int value)
    {
        this->value = value;
    }
    void show()
    {
        cout<<"the value : "<<value<<endl;
    }
};
int main ()
{
    ClassA a;
    a.seta(3);
    a.show();
    cout<<"a:"<<&a<<endl;
    ClassA b;
    b.seta(4);
    b.show();
    cout<<"b:"<<&b<<endl;
    b = a;
    a.show();
    b.show();
    cout<<"a:"<<&a<<", b"<<&b<<endl;
    b.seta(6);
    a.show();
    b.show();
    cout<<"a:"<<&a<<", b"<<&b<<endl;
}

运行结果：

the value : 3
a:0x22fefc
the value : 4
b:0x22fef8
the value : 3
the value : 3
a:0x22fefc, b0x22fef8
the value : 3
the value : 6
a:0x22fefc, b0x22fef8

Process returned 0 (0x0)   execution time : 0.132 s
Press any key to continue.