On the variable parameter _java in Java

Variable parameters

A variable parameter is a method that can receive any number of arguments! For example: Fun (), fun (1), Fun (1,1), Fun (1,1,1). You may think that this is a method overload, but this is not an overload, you think how many methods overload can overload, and the fun () method can pass any number of parameters, you can overload so many methods?

2.1 Defining variable parameter methods

Public voidfun (int ... arr) {}

The parameter type of the above method fun () is int ..., where "..." is not an ellipsis, but rather a way of defining the parameter type. Parameter arr is the variable parameter type. You can interpret the above code as: public void Fun (int[] arr).

public int sum1 (int[] arr) {
    int sum = 0;
    for (int i = 0; i < arr.length i++) {
      sum + + arr[i];
    }
    return sum;
  }

public int sum2 (int ... arr) {
    int sum = 0;
    for (int i = 0; i < arr.length i++) {
      sum + + arr[i];
    }
    return sum;
  }

You might think, "int[]" and "int ..." is no different, just "int ..." is a new way of defining an array parameter. Then I should congratulate you! Yes, that's the right thing to understand! Note, however, that only int can be used in the method's formal parameters ... To replace int[].

2.2 Calling a method with variable parameters

Calls to Sum1 () and sum2 () two methods:

SUM1 (New int[]{1,2,3});
Sum2 (New int[]{1,2,3});

It doesn't look any different! But there is another way to invoke sum2:

Sum2 ();

SUM2 (1);

SUM2 (1,2);

Sum2 (1,2,3);

This may seem like using any number of arguments to invoke the Sum2 () method, which is the benefit of invoking the method with variable parameters.

2.3 Compiler "Two processing"

The result of the compiler's "two machining" definition of the Sum2 method is:

public int sum2 (int[] arr) {
    int sum = 0;
    for (int i = 0; i < arr.length i++) {
      sum + + arr[i];
    }
    return sum;
  }

Change "int ..." to "int[]" type.

The compiler's two load results for the Sum2 method call are:

SUM2 (new int[0]);
SUM2 (New int[] {1});
SUM2 (New int[] {1, 2});
SUM2 (New int[] {1, 2, 3});

Conclusion: the variable parameter is actually an array type, but it is convenient to invoke the method, and the compiler helps us to pass multiple arguments to the formal parameter in an array.

2.4 Limitations of the variable parameter method

L A method can only have one variable parameter at most;

L The variable parameter must be the last parameter of the method.

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