Java中的复制构造函数-yiteyi-C++库

先决条件—— Java中的构造函数与C++一样，java也支持复制构造函数。但是，与C++不同，java不创建一个默认拷贝构造函数，如果你不自己编写。

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下面是一个示例Java程序，展示了复制构造函数的简单用法。

JAVA

                         // filename: Main.java                       
           
                         class                                     Complex {                       
           
                                                 private                                     double                                     re, im;                       
                                   
                                                 // A normal parameterized constructor                       
                                                 public                                     Complex(                                     double                                     re,                                     double                                     im) {                       
                                                 this                                     .re = re;                       
                                                 this                                     .im = im;                       
                                                 }                       
                                   
                                                 // copy constructor                       
                                                 Complex(Complex c) {                       
                                                 System.out.println(                                     "Copy constructor called"                                     );                       
                                                 re = c.re;                       
                                                 im = c.im;                       
                                                 }                       
                                   
                                                 // Overriding the toString of Object class                       
                                                 @Override                       
                                                 public                                     String toString() {                       
                                                 return                                     "("                                     + re +                                     " + "                                     + im +                                     "i)"                                     ;                       
                                                 }                       
                         }                       
           
                         public                                     class                                     Main {                       
           
                                                 public                                     static                                     void                                     main(String[] args) {                       
                                                 Complex c1 =                                     new                                     Complex(                                     10                                     ,                                     15                                     );                       
                                   
                                                 // Following involves a copy constructor call                       
                                                 Complex c2 =                                     new                                     Complex(c1);                       
           
                                                 // Note that following doesn't involve a copy constructor call as                       
                                                 // non-primitive variables are just references.                       
                                                 Complex c3 = c2;                       
           
                                                 System.out.println(c2);                                     // toString() of c2 is called here                       
                                                 }                       
                         }                       

输出：

Copy constructor called(10.0 + 15.0i)

现在尝试以下Java程序：

JAVA

                         // filename: Main.java                       
           
                         class                                     Complex {                       
           
                                                 private                                     double                                     re, im;                       
           
                                                 public                                     Complex(                                     double                                     re,                                     double                                     im) {                       
                                                 this                                     .re = re;                       
                                                 this                                     .im = im;                       
                                                 }                       
                         }                       
           
                         public                                     class                                     Main {                       
                                   
                                                 public                                     static                                     void                                     main(String[] args) {                       
                                                 Complex c1 =                                     new                                     Complex(                                     10                                     ,                                     15                                     );                       
                                                 Complex c2 =                                     new                                     Complex(c1);                                     // compiler error here                       
                                                 }                       
                         }                       

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