仅使用 if/else 在 Java 中按降序排列的数字

Question

How can I create a java program using only if / else to order 3 numbers in descending order. I can not use for processes or array. Numbers are entered by the user. Here's what i have so far. What should i do, is the user enters two integers that are the same? The code can only display one output.

    import java.util.Scanner; 
public class DescendingOrder
{
   public static void main(String [] args)
   {
      //variable dec.
      int a;
      int b;
      int c;
      Scanner kbd = new Scanner(System.in);

      //user prompt
      System.out.println("Please enter three integers");
      a=kbd.nextInt();
      b=kbd.nextInt();
      c=kbd.nextInt();

      //program output
      if (a>=b && b>=c && a>=c)
      {
         System.out.println("a b c");
      }

      if (a>=c && c>=b && a>=b )
      {   
         System.out.println("a c b");
      }   

      if (b>=a && a>=c && b>=c)
      {
         System.out.println("b a c");
      }

      if (b>=c && c>=a && b>=c)
      {      
          System.out.println("b c a");
      }

      if(c>=a && a>=b && c>=b)
      {
          System.out.println("c a b");
      }

      if (c>= b && b>=a && c>=a)
      {
         System.out.println("c b a"); 
      }   


   }
}

Answer 1

A simpler way you can do it is

if (a < b)
{
    int temp = a;
    a = b;
    b = temp;
}

if (b < c)
{
    int temp = b;
    b = c;
    c = temp;
}


if (a < b)
{
    int temp = a;
    a = b;
    b = temp;
}
System.out.println(a + " " + b + " " + c);

If two numbers are the same it doesn't really matter, as 90 45 45 is the same as 90 45 45. (In the case of your code as written, however, you are correct in noticing that it does matter. You could fix this by changing all your if statements except the first one into else-if)

Answer 2

This question seems to be a thought exercise so consider this answer an alternative to the other correct answers for your consideration. Here my enterprise-y solution.

Step 0, refactor your code to make it testable and stub out the method that will do the actual work:

import static java.lang.System.in;
import static java.lang.System.out;

import java.util.Scanner;

public class DescendingOrder {

    public static final void main(final String... args) { // unavoidable use of an array, please don't dock points
        try (final Scanner kbd = new Scanner(in)) { // always close your Closeables
            final int a = kbd.nextInt();
            final int b = kbd.nextInt();
            final int c = kbd.nextInt();
            final DescendingOrder calculator = new DescendingOrder();
            out.println(calculator.order(a, b, c));
        }
    }

    public String order(final int a, final int b, final int c) {
        return null;
    }
}

Step 1, write a unit test:

import static java.lang.Integer.MAX_VALUE;
import static java.lang.Integer.MIN_VALUE;
import static org.junit.Assert.assertEquals;

import org.junit.Before;
import org.junit.Test;

public class DescendingOrderTest {

    private DescendingOrder orderer;

    @Before
    public void setUp() throws Exception {
        orderer = new DescendingOrder();
    }

    @Test
    public final void testOrderABC() {
        final String result = orderer.order(MAX_VALUE, 0, MIN_VALUE); // don't forget the edge cases
        assertEquals(MAX_VALUE + " " + 0 + " " + MIN_VALUE, result);
    }

    @Test
    public final void testOrderACB() {
        final String result = orderer.order(13, 5, 8);
        assertEquals("13 8 5", result);
    }

    @Test
    public final void testOrderBAC() {
        final String result = orderer.order(4, 8, 2);
        assertEquals("8 4 2", result);
    }

    @Test
    public final void testOrderBCA() {
        final String result = orderer.order(-8, -2, -4); // don't forget negative numbers
        assertEquals("-2 -4 -8", result);
    }

    @Test
    public final void testOrderCAB() {
        final String result = orderer.order(1, -5, 5);
        assertEquals("5 1 -5", result);
    }

    @Test
    public final void testOrderCBA() {
        final String result = orderer.order(MAX_VALUE, 0, MIN_VALUE);
        assertEquals(MAX_VALUE + " " + 0 + " " + MIN_VALUE, result);
    }

    @Test
    public final void testAllSame() {
        final String result = orderer.order(53, 53, 53);
        assertEquals("53 53 53", result);
    }
}

Step 2, iteratively implement order until your tests pass:

    public String order(final int a, final int b, final int c) {
        if (a > b && a > c) {
            return a + " " + order(b, c);
        } else if (b > a && b > c) {
            return b + " " + order(a, c);
        }
        return c + " " + order(a, b);
    }

    protected String order(final int x, final int y) {
        if (x > y) {
            return x + " " + y;
        }
        return y + " " + x;
    }

It might not be the most computationally efficient, but I kept the method sizes small so it is clear what the code is meant to accomplish. I also do not need to scan through six scenarios to see that it is correct. If I assume that order( int, int ) is correct, then I only need to work through three scenarios to see that order( int, int, int ) is correct.

Obviously, this is overkill. But those constraints would never really exist.

Answer 3

I think your code was fine you were just printing wrong. You have to understand that a,b,c are variable of type int. when you use the + operator with two ints it performs an addition. If you use the + operator with an int and with a string it produces a concatenation. The int 'calls' to string turning the int into a string which produces String + String = concatenation. Anyways, I think this is what you wanted. Let me know if this is what you wanted.

    import java.util.Scanner; 
public class Stackoverflow
{
   public static void main(String [] args)
   {
      //variable dec.
      int a;
      int b;
      int c;
      Scanner kbd = new Scanner(System.in);

      //user prompt
      System.out.println("Please enter three integers");
      a=kbd.nextInt();
      b=kbd.nextInt();
      c=kbd.nextInt();

      //program output
      if (a>=b && b>=c && a>=c)
      {
         System.out.println(a+" "+b+" "+c);
      }

      if (a>=c && c>=b && a>=b )
      {   
         System.out.println(a+" "+c+" "+b);
      }   

      if (b>=a && a>=c && b>=c)
      {
         System.out.println(b+" "+a+" "+c);
      }

      if (b>=c && c>=a && b>=c)
      {      
          System.out.println(b+" "+c+" "+a);
      }

      if(c>=a && a>=b && c>=b)
      {
          System.out.println(c+" "+a+" "+b);
      }

      if (c>= b && b>=a && c>=a)
      {
         System.out.println(c+" "+b+" "+a); 
      }   


   }
}