Question

我开始学习考试并用方法做一些练习课程，我的脑海里现在空白了。我想知道如何初始化n1，n2，n3和n4。我将它们设置为0但返回语句仅返回0。

public class LargestOfIntegers2
{
    public static int findLargest(int n1, int n2, int n3, int n4)
    {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter the first integer --> ");
        n1 = scan.nextInt();
        System.out.print("Enter the second integer --> ");
        n2 = scan.nextInt();    
        System.out.print("Enter the third integer --> ");
        n3 = scan.nextInt();    
        System.out.print("Enter the fourth integer --> ");
        n4 = scan.nextInt();    

        if(n1>n2 && n1 > n3 && n1 > n4)
            return n1;
        else if(n2 > n1 && n2 > n3 && n2 > n4)
           return n2;
        else if(n3>n1 && n3>n2 && n3>n4)
            return n3;
        else
            return n4;
    }

    public static void main(String[] args) {
        int n1, n2, n3, n4;

        findLargest(n1, n2, n3, n4);
        if(n1>n2 && n1 > n3 && n1 > n4)
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n1);
        else if(n2 > n1 && n2 > n3 && n2 > n4)
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n2);
        else if(n3>n1 && n3>n2 && n3>n4)
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n3);
        else
            System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n4);

    }
}

Answer 1

您的代码无效的主要原因：

public static void main(String[] args) {
    int n1, n2, n3, n4;

    findLargest(n1, n2, n3, n4);    <--- YOU DID NOT STORE THE RETURNED VALUE
    if(n1>n2 && n1 > n3 && n1 > n4)
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n1);
    else if(n2 > n1 && n2 > n3 && n2 > n4)
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n2);
    else if(n3>n1 && n3>n2 && n3>n4)
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n3);
    else
        System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n4);

}

要么：

//prompt user input for n1, n2, n3, n4 first
System.out.println(findLargest(n1,n2,n3,4));

或

//prompt user input for n1, n2, n3, n4 first int largest = findLargest(n1,n2,n3,n4); System.ouot.println(largest);

我相信这会让你的代码有效。当然，在调用方法之前，不应在方法中提示用户输入，而应在方法之外提示它。

Java方法如何传递其值的说明：

public static void main(String[] args) { int n = 100; someMethod(n); System.out.println(n); //n will still be 100; } public static void someMethod(int n1) { n1 = 999; }

为什么主{0}中的n仍然是100，而不是999.这是因为Java按值传递所有内容。对于基本类型，传递的值是实际值本身。意味着将实际值的副本传递给方法。制作了一份副本。因此n1（范围： someMethod ）只是n的副本（范围：主要）。 n1 上的更改不会影响 n。

为您提供额外的帮助：

如果您传递了4个变量n1, n2, n3, n4。为什么要求用户在方法中再次输入4个值？

这样做将“无效”从方法的调用者传入的n1，n2，n3，n4的值。

顺便说一下，有很多简单的方法可以实现这一点。通过不触及数组，您可以简单地执行此操作：

public static int findLargest(int n1, int n2, int n3, int n4) { return Math.max(Math.max(n1,n2), Math.max(n3,n4)); }

Answer 2

这是您的代码将执行的操作：这将得到新的n1和n2以及n3和n4，并将它们设置为等于你传递的值

  public static int findLargest(int n1, int n2, int n3, int n4){
 {

您传递了未初始化的值，因此它们未初始化然后用用户输入初始化它们（当你的变量是本地的时候，这个方法以外的任何一个变化）你找到最大的并返回它你的代码在任何地方都存储了这个价值

 int thelargest=findLargest(n1, n2, n3, n4);

会存储它

然后尝试比较UNINITIALIZED INTS，因为findlargest的方法无法看到n1 n2 n3 n4，因为没有通过引用来修复代码以执行我认为你想做的事情

 static int n1,n2,n3,n4;
  public static void findLargest()

{
Scanner scan = new Scanner(System.in);
System.out.print("Enter the first integer --> ");
n1 = scan.nextInt();
System.out.print("Enter the second integer --> ");
n2 = scan.nextInt();    
System.out.print("Enter the third integer --> ");
n3 = scan.nextInt();    
System.out.print("Enter the fourth integer --> ");
n4 = scan.nextInt();    
//nothing is listening for these numbers anyway why bother with it
 // if(n1>n2 && n1 > n3 && n1 > n4)
 //   return n1;
 // else if(n2 > n1 && n2 > n3 && n2 > n4)
  // return n2;
 // else if(n3>n1 && n3>n2 && n3>n4)
//      return n3;
 // else
 //    return n4;
}

public static void main(String[] args) {
//int n1, n2, n3, n4;

findLargest();
if(n1>n2 && n1 > n3 && n1 > n4)
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n1);
else if(n2 > n1 && n2 > n3 && n2 > n4)
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 + ", the largest integer is " + n2);
else if(n3>n1 && n3>n2 && n3>n4)
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4 +   ", the largest integer is " + n3);
else
    System.out.println("Out of the numbers " + n1 + ", " + n2 + ", " + n3 + ", " + n4         +    ", the largest integer is " + n4);

}

}

Answer 3

变量n1到n4将在findLargest函数中设置，但只在其本地副本中设置，更改将永远不会“回显”回{{1}功能。这是你的主要问题，因为main中的变量因此没有被设置。

最好在函数中询问每个变量并返回它，然后通过获取返回值正确使用main。那会是这样的：

findLargest

您可以看到我也对import java.util.Scanner; public class Test { public static int getNum(Scanner sc, String desc) { System.out.print("Enter the " + desc + " integer --> "); return sc.nextInt(); } public static int findLargest(int n1, int n2, int n3, int n4) { if (n1 >= n2 && n1 >= n3 && n1 >= n4) return n1; if (n2 >= n3 && n2 >= n4) return n2; if (n3 >= n4) return n3; return n4; } public static void main(String[] args) { Scanner scan = new Scanner(System.in); int a = getNum(scan, "first"); int b = getNum(scan, "second"); int c = getNum(scan, "third"); int d = getNum(scan, "fourth"); int x = findLargest(a, b, c, d); System.out.println("max(" + a + "," + b + "," + c + "," + d + ") = " + x); } }函数进行了更改，以最大限度地减少比较。例如，如果您在没有返回的情况下完成第一个findLargest语句，则知道 if与进一步比较无关，因为它小于至少一个其他值。

如何解决变量可能没有初始化错误

3 个答案: