Java 后缀增量

Question

I understand that x=y++ is essentially shorthand for y=x and x=x+1.

However, I fail to see in what scenario it can be used. Why would I increment a variable and assign its old value to a new variable.

Answer 1

If you don't find a need for something, it's best not to use it. Remember, don't code as cleverly as you can. Dumb it down so that you can debug it.

However, since it is a feature, of course you can make use of it.

import java.util.*;
public class MyClass {
    public static void main(String args[]) {
      ArrayList<Integer> l = new ArrayList<>();
      l.add(0); l.add(1); l.add(2);
      int s = 0;
      while (s<l.size()-1) {
          System.out.println(l.get(++s));
      }
    }
}

This prints 1, 2

import java.util.*;
public class MyClass {
    public static void main(String args[]) {
      ArrayList<Integer> l = new ArrayList<>();
      l.add(0); l.add(1); l.add(2);
      int s = 0;
      while (s<l.size()) {
          System.out.println(l.get(s++));
      }
    }
}

This prints 0, 1, 2

Can do it on arrays too. arr[i++], a[++i], a[i--], a[--i] You can do something like while(i++ > 0) too.

It serves mainly two purposes I guess.

1. Compress multiple extremely short lines in 1. (This is actually handy in coding tests if you use Java)
2. When you messed up and have to add 1 and subtract 1 frantically to a variable, you can use ++v, v++, --v, v-- instead of bunch of v-1, v+1, v+2, v-2, (v-1)+1... (although I think you are more likely to make a wrong program by using postfix, prefix in these cases)

If you really want to use it,.. at least avoid using 2 or more post/prefix notations on same variable on the same statement.. It is really prone to error. For example,

x++ - ++x; // -2
++x - ++x; // -1
x++ - x++; // -1
++x - x++; // 0

I can explain why these four statements are evaluated to such results, but I wouldn't use those patterns in coding tests or any development whatsoever.