Logical gates with integer values

Question

I have created this code for both boolean and integer values to display a truth table for an "AND","OR","XOR", "NOT" gate. However I think that my code needs reviewing as it could be simplified.

public class LogicalOpTable {
 public static void main(String[] args){
 boolean p,q;
 System.out.println("P\tQ\tAND\tOR\tXOR\tNOT");
 p = false;
 q = false;
 System.out.print(p + "\t" + q + "\t" + (p&&q) + "\t");
 System.out.println((p||q)+"\t"+(p^q)+"\t"+(!p));
 p = false;
 q = true;
 System.out.print(p + "\t" + q + "\t" + (p&&q) + "\t");
 System.out.println((p||q)+"\t"+(p^q)+"\t"+(!p));
 p = true;
 q = false;
 System.out.print(p + "\t" + q + "\t" + (p&&q) + "\t");
 System.out.println((p||q)+"\t"+(p^q)+"\t"+(!p));
 p = true;
 q = true;
 System.out.print(p + "\t" + q + "\t" + (p&&q) + "\t");
 System.out.println((p||q)+"\t"+(p^q)+"\t"+(!p));
 System.out.println();
 withBinary();
 }
 public static void withBinary(){
 System.out.println("A\tB\tAND\tOR\tXOR\tNOT");
 int a = 0;
 int b = 0;
 int and = a&b;
 int or = a|b;
 int xor = a^b;
 int not = a;
 if(a==0 && b == 0 )
 not = 1;
 System.out.println(a + "\t" + b + "\t" + and + "\t" + or + "\t" + xor + "\t" + (not));
 b=1;
 and = a&b;
 or = a|b;
 xor = a^b;
 not = a;
 if(a==0 && b == 1)
 System.out.println(a + "\t" + b + "\t" + and + "\t" + or + "\t" + xor + "\t" + (not));
 a=1; 
 b=0;
 not = b;
 and = a&b;
 or = a|b;
 xor = a^b;
 not = a;
 if(a==1 && b == 0)
 System.out.println(a + "\t" + b + "\t" + and + "\t" + or + "\t" + xor + "\t" + (not)); 
 a=1; 
 b=1;
 not = 0;
 and = a&b;
 or = a|b;
 xor = a^b;
 if(a==1 && b == 1)
 System.out.println(a + "\t" + b + "\t" + and + "\t" + or + "\t" + xor + "\t" + (not)); 
 }
}

• tkausl: I don't really get the point of this program. Has it any purpose other than print some debug-values?
• mp252: Its just a simple program to print out a truth table for the logic gates, once in boolean and then in integers. It was a question in a book. They already completed the boolean part, and then it says attempt to create a new logic table with the binary equivalent values.

Answer 1

First part

You want to iterate through all possible combinations of for a pair of booleans, so you can make the code reflect that explicitly and make it simpler:

 System.out.println("P\tQ\tAND\tOR\tXOR\tNOT");
 for (boolean p : new boolean[] {true, false}) {
 for (boolean q : new boolean[] {true, false}) {
 System.out.print(p + "\t" + q + "\t" + (p&&q) + "\t");
 System.out.println((p||q)+"\t"+(p^q)+"\t"+(!p));
 }
 }
 System.out.println();

Second part

You have something suspicious in your if statements. As you don't use braces, this code smells of a copy&paste bug:

 if(a==0 && b == 0 )
 not = 1;
 System.out.println(a + "\t" + b + "\t" + and + "\t" + or + "\t" + xor + "\t" + (not));

If the condition is met, it will execute the line not = 1;. The second line will be executed independently of the condition. I strongly suggest you use braces even for 1-line blocks, like this:

 if (a == 0 && b == 0) {
 not = 1;
 System.out.println(a + "\t" + b + "\t" + and + "\t" + or + "\t" + xor + "\t" + (not));
 }

This way you can avoid this kind of bugs.

Now, applying the same reasoning as with the previous method, you can rewrite it as:

 System.out.println("A\tB\tAND\tOR\tXOR\tNOT");
 for (int a : new int[] {0, 1}) {
 for (int b : new int[] {0, 1} ) {
 System.out.println(a + "\t" + b + "\t" + (a & b) + "\t" + (a | b) + "\t" + (a ^ b) + "\t" + ~a);
 }
 }

BUT What do you want to accomplish with the NOT operation? Do you mean the Bitwise Complement? I used that, but maybe you want a function that returns 0 when it's 1, and 1 when it's 0. In that case, you need to replace the ~a with something like (a == 0) ? 1 : 0.

So the whole code could be reduced to just:

public static void printTable() {
 System.out.println("P\tQ\tAND\tOR\tXOR\tNOT");
 for (boolean p : new boolean[]{true, false}) {
 for (boolean q : new boolean[]{true, false}) {
 System.out.print(p + "\t" + q + "\t" + (p&&q) + "\t");
 System.out.println((p||q)+"\t"+(p^q)+"\t"+(!p));
 }
 }
 System.out.println();
 System.out.println("A\tB\tAND\tOR\tXOR\tNOT");
 for (int a : new int[]{ 0, 1}) {
 for (int b : new int[]{0, 1} ) {
 System.out.println(a + "\t" + b + "\t" + (a & b) + "\t" + (a | b) + "\t" + (a ^ b) + "\t" + ~a);
 }
 }
}

• Diego Martinoia: You could even wrap your formatting "print" code in named method for enhanced readability.