Java的无效方法重载

重载方法是那些属于同一个类，具有相同名称但不同参数的方法。方法重载的概念来自多态。从字面上看，“poly”的意思是许多，而“morphism”的意思是形式。

考虑一个现实生活中的水是多晶型的例子，因为它可以有多种形式（固体、液体和气体）。同样，在Java，我们可以在同一个类中创建多个同名方法。在这里，我们将讨论Java的无效方法重载，但在此之前让我们简要回顾一下方法重载。

方法重载的条件

• 我们可以在同一个类中创建多个同名方法。
• 参数的数量、参数的顺序和参数的类型应该不同。

插图：方法重载

Java

// Java Program to Illustrate Method Overloading
  
// Main class
class GFG {
  
    // Method 1
    void show()
    {
        // Print statement
        System.out.println("Method to be overloaded.");
    }
  
    // Method 2
    // Overloading Method 1
    // by changing arguments
    void show(int x)
    {
        // Print statement
        System.out.println("Overloaded method:: 1");
    }
  
    // Method 3
    // Overloading show method by changing arguments
    void show(String a, int x)
    {
        System.out.println("Overloaded method:: " + x);
    }
  
    // Method 4
    // Overloading show method
    // by changing arguments
    void show(String a, int b, boolean c)
    {
        System.out.println("Overloaded method:: " + b);
    }
  
    // Method 5
    // Overloading Metohd 1 by
    // changing arguments as well as return type
    String show(String s)
    {
        // Print statement
        return "Overloaded method:: 5";
    }
  
    // Method 6
    // Main driver method
    public static void main(String[] args)
    {
        // Creating object of class inside main()
        GFG obj = new GFG();
  
        // Calling all methofs as defined above
        // to seek overloading concepts
        obj.show();
        obj.show(1);
        obj.show("String", 2);
        obj.show("String", 3, true);
        System.out.println(obj.show("String"));
        obj.show('a');
    }
}

输出-

Method to be overloaded.
Overloaded method:: 1
Overloaded method:: 2
Overloaded method:: 3
Overloaded method:: 5
Overloaded method:: 1

什么时候会出现无效方法重载的情况？

由于以下原因，会出现无效方法重载的情况：

1. 如果我们尝试调用多个具有相同名称和参数列表的方法。这可以从代码块 1 中得到证明。
2. 当我们尝试仅通过更改返回类型来重载方法时。这可以从代码块 2 中得到证明。

执行：

考虑下面给出的例子。当我们尝试调用“ add(1,2) ”方法时，编译器会感到困惑，因为没有这样的指令更喜欢 int 而不是 double ，反之亦然，结果，它会显示编译错误。

int add(int a, int b)
double add(int a, int b)

示例 1-A

Java

// Demo class
class Demo {
    // Programmer defined "mymethod"
    public int myMethod(int num1, int num2)
    {
        System.out.println("First myMethod of class Demo");
        return num1 + num2;
    }
    // Trying to overload "mymethod"
    public int myMethod(int num3, int num4)
    {
        System.out.println("Second myMethod of class Demo");
        return num4 - num3;
    }
}
// Driver class
class GFG {
    // main method
    public static void main(String args[])
    {
        Demo obj1 = new Demo();
        obj1.myMethod(1, 2);
        obj1.myMethod(3, 4);
    }
}

输出：

prog.java:7: error: method myMethod(int,int) is already defined in class Demo
    public int myMethod(int num3, int num4)
               ^
1 error

示例 1-B

Java

// Java Program to Illiustarte No Roleplay of Returntype
// Even changed in Method Overloading
  
// Main class
class GFG {
  
    int a, b;
  
    // Declared method
    void add(int x, int y)
    {
        // This refers to current instance itself
        this.a = x;
        this.b = y;
  
        // Printing the sum
        System.out.println("SUM:: " + (a + b));
    }
  
    // Method 2
    // To add numbers
    // Overloading the above declared method by
    // changing the return type only
    double add(int x, int y)
    {
        this.a = x;
        this.b = y;
        return a + b;
    }
  
    // Method 3
    // Main method method
    public static void main(String[] args)
    {
        // Creating object of class inside main()
        GFG obj = new GFG();
  
        // Calling add() method by passing
        // custom inputs as parameters
        obj.add(5, 2);
  
        // Trying printing the sum
        System.out.println("Sum:: " + obj.add(3, 4));
    }
}

输出：

prog.java:8: error: method add(int,int) is already defined in class GFG
  double add(int x,int y){
         ^
prog.java:17: error: 'void' type not allowed here
      System.out.println("Sum:: "+obj.add(3,4));
                                         ^
2 errors

Conclusion:  We can not call more than one method with the same name and argument list. Return type of method will not play any roles in method overloading, in java it is not possible to achieve overloading by changing the return type of the method only.