Logic of Java Operators && and ||

Question

Hello dear Programmers,

I have a String String input = "30.09.1993"; Then i want to save all numbers in this string in an array(Only numbers!). The "." are at index 2 and 5 so i want to skip these parts of my string in my loop with an if-statement.

I fixed my problem and everything works fine but I'm confused with the logic of the && and || operators.

This is my working code:

String input = "30.09.1993";
int[] eachNumbers = new int[8];

int x = 0;
for(int i = 0; i <= 9; i++){
    if(i != 2 && i != 5){
       eachNumbers[x] = Integer.parseInt(input.substring(i, i+1));
       x++;
    }
}

And this is the code which doesnt work:

String input = "30.09.1993";
int[] eachNumbers = new int[8];

int x = 0;
for(int i = 0; i <= 9; i++){
    if(i != 2 || i != 5){
       eachNumbers[x] = Integer.parseInt(input.substring(i, i+1));
       x++;
    }
}

The only difference between these two code snippets are the operators in the if-clause.

I thought that the results for these operators are:

&& operator:

false + false = false
true  + false = false
false + true  = false
true  + true  = true

|| operator:

false + false = false
true  + false = true
false + true  = true
true  + true  = true

So in my opinion the second code snippet should work and the first should throw a NumberFormatException. But thats not the case.

I'm sure there are some better solutions for what im doing but my question is only about the logic in my if-statement. Can someone explain me the logic behind this? I'm totally confused and thankful for every helping answer.

Greetings Lukas Warsitz

Logic of Java Operators && and ||

7 Answers