Computer Science 15-110, Spring 2010
Class Notes: Data and Expressions (1 of 3)
Data and Expressions (1 of 3)
class MyCode { public static void main(String[] args) { int x = 3; System.out.println(x); } }
Same, but with a nicer UI
class MyCode { public static void main(String[] args) { int x = 3; System.out.println("x = " + x); } }
class MyCode {
public static void main(String[] args) {
System.out.println("x = " + x); // ERROR! No such variable as x
}
}
class MyCode { public static void main(String[] args) { int x; // declare the variable x = 5; // initialize it (assign it its first value) System.out.println("x = " + x); } }
class MyCode { public static void main(String[] args) { int x; x = 1; System.out.println("x = " + x); // prints "x = 1" x = 2; System.out.println("x = " + x); // prints "x = 2" } }
class MyCode {
public static void main(String[] args) {
int x; // declared, but not assigned a value
System.out.println("x = " + x); // ERROR! x is not initialized
}
}
class MyCode { public static void main(String[] args) { int x = 1; int y = 2; System.out.println("x = " + x); System.out.println("y = " + y); } }
class MyCode { public static void main(String[] args) { int x = 1, y = 2; System.out.println("x = " + x); System.out.println("y = " + y); } }
class MyCode {
public static void main(String[] args) {
int x = 1, y = 2;
System.out.println("x = " + x);
System.out.println("y = " + y);
System.out.println("x + y = " + (x + y));
}
}
Same, but with a nicer UI
class MyCode { public static void main(String[] args) { int x = 1, y = 2; System.out.println("x = " + x); System.out.println("y = " + y); System.out.println("x + y = " + x + " + " + y + " = " + (x + y)); } }
class MyCode {
public static void main(String[] args) {
System.out.println(2+3*4); // prints 14, not 20
}
}
class MyCode { public static void main(String[] args) { int x = 1*1000*1000*1000; // 1 billion int y = 2*1000*1000*1000; // 2 billion System.out.println(x + y); // Prints -1294967296 } }
class MyCode { public static void main(String[] args) { System.out.println("20/3 = " + (20/3)); System.out.println(" 6/3 = " + ( 6/3)); System.out.println(" 5/3 = " + ( 5/3)); System.out.println(" 2/3 = " + ( 2/3)); } }
class MyCode { public static void main(String[] args) { System.out.println(" 7%3 = " + (7%3)); System.out.println(" 6%3 = " + (6%3)); System.out.println(" 5%3 = " + (5%3)); System.out.println(" 3%3 = " + (3%3)); System.out.println(" 2%3 = " + (2%3)); System.out.println(" 0%3 = " + (0%3)); System.out.println(" 3%0 = " + (3%0)); } }
class MyCode { public static void main(String[] args) { int x = 5; System.out.println(x); // 5 x++; System.out.println(x); // 6 ++x; System.out.println(x); // 7 x--; System.out.println(x); // 6 --x; System.out.println(x); // 5 } }
class MyCode { public static void main(String[] args) { int x = 5; System.out.println(x); // 5 x += 2; System.out.println(x); // 7 x *= 2; System.out.println(x); // 14 x %= 9; System.out.println(x); // 5 x /= 2; System.out.println(x); // 2 x -= 5; System.out.println(x); // -3 } }
class MyCode { public static void main(String[] args) { System.out.println(Math.abs(4)); // 4 System.out.println(Math.abs(-4)); // 4 System.out.println(Math.min(3, 2)); // 2 System.out.println(Math.min(2, 3)); // 2 System.out.println(Math.max(3, 2)); // 3 System.out.println(Math.max(2, 3)); // 3 // We can use these in expressions, too: int x = Math.min(5, -13); int y = Math.max(x, x/2); int z = Math.abs(x) + Math.abs(y); System.out.println(x); System.out.println(y); System.out.println(z); } }
class MyCode { public static void main(String[] args) { boolean b = true; System.out.println(b); // prints true System.out.println(false); // prints false } }
class MyCode { public static void main(String[] args) { System.out.println(5 == 4); System.out.println(5 == 5); System.out.println(5 != 4); System.out.println(5 != 5); } }
class MyCode { public static void main(String[] args) { System.out.println(5 < 4); System.out.println(5 > 4); System.out.println(5 < 5); System.out.println(5 <= 5); System.out.println(5 >= 5); System.out.println(5 > 5); } }
class MyCode { public static void main(String[] args) { System.out.println("&& (AND)"); System.out.println(true && true ); System.out.println(true && false); System.out.println(false && true ); System.out.println(false && false); System.out.println("|| (OR)"); System.out.println(true || true ); System.out.println(true || false); System.out.println(false || true ); System.out.println(false || false); System.out.println("! (NOT)"); System.out.println( !true ); System.out.println( !false ); } }
class MyCode { public static void main(String[] args) { int x = 0, y = 0; System.out.println((y != 0) && ((x/y) != 0)); // Works! System.out.println(((x/y) != 0) && (y != 0)); // Crashes! } }
Once again, using the "or" operator ( || )
class MyCode { public static void main(String[] args) { int x = 0, y = 0; System.out.println((y == 0) || ((x/y) == 0)); // Works! System.out.println(((x/y) == 0) || (y == 0)); // Crashes! } }
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