AboutOperators.java

#set( $symbol_pound = '#' )
#set( $symbol_dollar = '$' )
#set( $symbol_escape = '\' )
package beginner;

import com.sandwich.koan.Koan;
import static com.sandwich.koan.constant.KoanConstants.__;
import static com.sandwich.util.Assert.assertEquals;

public class AboutOperators {

	@Koan
	public void plusPlusVariablePlusPlus(){
		int i = 1;
		assertEquals(++i, __);
		assertEquals(i, __);
		assertEquals(i++, __);
		assertEquals(i, __);
	}
	
	@Koan
	public void shortCircuit() {
		int i = 1;
		int a = 6; // Why did we use a variable here?
		// What happens if you replace 'a' with '6' below?
		// Try this with an IDE like Eclipse...
		if ( (a < 9 ) || (++i < 8) )  i = i + 1;
		assertEquals(i, __);
	}
	
	@Koan
	public void fullAnd(){
		int i = 1;
		if ( true & (++i < 8) )  i = i + 1;
		assertEquals(i, __);
	}
	
	@Koan
	public void shortCircuitAnd(){
		int i = 1;
		if ( true && (i < -28) )  i = i + 1;
		assertEquals(i, __);
	}
	
	@Koan
	public void aboutXOR() {
		int i = 1;
		int a = 6;
		if ( (a < 9 ) ^ false)  i = i + 1;
		assertEquals(i, __);
	}
	
	@Koan
	public void dontMistakeEqualsForEqualsEquals() {
		int i = 1;
		boolean a = false;
		if (a = true) i++;
		assertEquals(a, __);
		assertEquals(i, __);
		// How could you write the condition 'with a twist' to avoid this trap?
	}
	
	@Koan
	public void aboutBitShiftingRightShift() {
		int rightShift = 8;
		rightShift = rightShift >> 1; 
		assertEquals(rightShift, __);
	}
	
	@Koan
	public void aboutBitShiftingLeftShift() {
		int leftShift = 0x80000000; // Is this number positive or negative?
		leftShift = leftShift << 1;
		assertEquals(leftShift, __);
	}
	
	@Koan
	public void aboutBitShiftingRightUnsigned() {
		int rightShiftNegativeStaysNegative = 0x80000000;
		rightShiftNegativeStaysNegative = rightShiftNegativeStaysNegative >> 4;
		assertEquals(rightShiftNegativeStaysNegative, __);
		int unsignedRightShift = 0x80000000; // always fills with 0
		unsignedRightShift >>>= 4; // Just like +=
		assertEquals(unsignedRightShift, __);
	}
	
}