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Selection Statements o Alternative execution paths based on the result of a conditional expression o Decision making statements
Conditional Expression o Boolean expression/logical expression o Has a value of true or false o relational operators (ro): < > <= >= == != Variable ro variable a < b a==b a!=b decimals and == doesn’t always work when expected due to rounding the relational operators only work on primitive data types (int, double, boolean, char) not on class types such as String
String Z = “CS”; String R = new String (Z); String X = R;
When = is used the system looks to see if the string exists and if so points the reference to it
CS
CpE Dual
String s1 = new String (“Happy”); String s2 = “Happy”;
s s
Consider String s2 =”Happy”; String s1 = new “Happy”;
s s
Comparing Class Objects o == and != compare references - They determine if two class objects “point” to the same memory not if the data is equivalent - To compare the data objects of class references .equals - S.equals(R) - S.equalsIgnoreCase(R) - For
Strings
Can’t change the value of a string through assignment
String s =”abc”;
Can’t later say s=”xyz”; you would have to say s=new String (“xyz”);
Happy
Happy Happy
Evaluate the condition Æ if true execute 1st^ block, if false execute the else block
Homework set 4: Write the JAVA statements to accomplish the following
a). If item is non-zero, multiply product by item and save the result in product ; otherwise, skip the multiplication. Either way, display the value of product.
b). Store the absolute difference of x and y in y , where the absolute difference is (x-y) or (y-x) whichever is positive.
c). If x is 0, add 1 to zeroCount. If x is negative add x to minusSum. If x is greater than 0 add x to plusSum.
d). Write a method sameSign() that, given two double parameters return true if they are of the same sign and false if they have difference signs.
e). Rewrite sameSign() which returns the actual sign ‘+’ or ‘-‘ if they are the same sign and a blank if they are different signs.
Multiple Alternative Decisions o Need more than 2 alternatives Example 0 + - if (x==) stmt //x = else if (x > 0) stmt //x > 0 else stmt //x<
Membership dues set on a sliding salary scale if (salary <=10000) dues= .05 * salary; else if (salary <= 30000) dues = .08 * salary; else if ( salary <= 50000) dues = .1 * salary; else if (salary <= 70000) dues = .15 * salary; else dues = .2 * salary
o Comparison of using separate if’s o 0 + - if (x ==0) stmt if (x<0) stmt if(x>0) stmt
each is tested when if one is true the others are not true and should not be tested – else construct does not retest o Membership dues if (salary < 10000) dues = if (salary >=10000 && salary < 30000) dues = if (salary >=30000 & salary < 500000) dues = if (salary >=50000 & salary <700000) dues = if (salary >=70000) dues
switch (n) { case 1: case 2:System.out.print (“Buckle my Shoe”); break; case 3: case4: System.out.print(“Shut the Door”); break; case 5: case 6: System.out.print (“Pick up Sticks”); break; case 7: case 8: System.out.print (“Shut the Gate”); break; case 9: case 10: System.out.print (“Start Again”); break; default: System.out print(“Invalid value”); }
