Study Guide - More Advanced Java

Consider two boolean variables a and b. Which of the following best refactors this code?

• if(a && b) System.out.println("a");

• if(a || b) System.out.println("a");

• if(a) System.out.println("a");

• if(b) System.out.println("b");

Answer explanation

Because the same code executes whether b is true or false, it can be ignored entirely. Therefore, the code can be simplified to if(a) System.out.println("a");

Consider two boolean variables a and b. Which of the following best refactors this code?

• if(b) System.out.println(a?"b":"a");

• if(b) System.out.println(a?"a":"b");

• if(a) System.out.println(b?"b":"a");

• if(a) System.out.println(b?"a":"b");

Answer explanation

The value given to System.out.println() depends on if b is true or false. Therefore, this can be simplified to if(a) System.out.println(b?"b":"a");

Consider three boolean variables a, b, and c. Which of the following best refactors this code?

• if(a?b:c) System.out.println("Hello!");

• if((a && b) || (!a && c)) System.out.println("Hello!");

• if(b || c) System.out.println("Hello!");

• if(b?a:c&&!a) System.out.println("Hello!");

Answer explanation

Many of these will function the same as in the image, but if(a?b:c) System.out.println("Hello!"); is the simplest.

Consider three boolean variables a, b, and c. Which of the following best refactors this code?

• if(a && (b==c)) System.out.print("Hello!");

• if(a && ((b&&c) || !b)) System.out.print("Hello!");

• if(a && ((b&&c) || (!b&&!c))) System.out.print("Hello!");

• if((b&&c) || !b) System.out.print("Hello!");

Answer explanation

In the inner if-statement, the else if block is only triggered if b is false. Therefore, "Hello!" will be printed only if b and c are both true, or if b and c are both false. Therefore, if(a && (b==c)) System.out.print("Hello!"); will refactor this code.

Consider three boolean variables a, b, and c. Which of the following best refactors this code?

• if(a && (b==c)) System.out.println(b?"Hello!":"Goodbye.");

• if(a) {

  if(b&&c) System.out.println("Hello!");

  else if(!b && !c) System.out.println("Goodbye.");

  }

• if(a && ((b&&c) || !c)) System.out.println(c?"Hellol":"Goodbye.");

• if(a) {

  if((b&&c) || !c) System.out.println(c?"Hello!":"Goodbye.");

  }

Answer explanation

In fact, all of these will function identically. However, if(a && (b==c)) System.out.println(b?"Hello!":"Goodbye."); is the most simplified. Only if b and c are both true or both false will something be printed. What gets printed depends on if b (and therefore c) is true, or if it's false.

Which of the following methods will get the union u of two ArrayLists a and b? Select all that apply.

• Adding everything from a to u, and everything from b to u.

• Deleting everything from a that's in b, then adding everything from a and b to u.

• Deleting everything from b that's in a, then adding everything from a and b to u.

• Adding everything from a to u that's not also in b, then adding everything from b to u that's not also in a.

Answer explanation

Adding everything from a to u, and everything from b to u will doubly count the intersection of a and b. Adding everything from a to u that's not also in b, then adding everything from b to u that's not also in a will not include the intersection of a and b. Of these options, only deleting everything from a that's in b, then adding everything from a and b to u and deleting everything from b that's in a, then adding everything from a and b to u will work as intended.

Consider two Squares s and t. Which of the following will swap the values of s and t?

• Square u = s; s = t; t = u;

• Square u = s; t = u; s = t;

• Square u = t; s = u; t = s;

• Square u = t; t = u; s = t;

Consider a ChessPiece k. Suppose as part of a routine which calculates chess moves, k must be temporarily deleted before calling function f(), and then restored afterward. Which of the following will do this?

• ChessPiece m = k; k = null; f(); k = m;

• k = null; f(); k = m;

• ChessPiece m = k; f(); k = m;

• ChessPiece m; k = m; f(); m = k;

Answer explanation

If an Object must be temporarily deleted, it can be moved to a temporary Object of the same type to be restored from later. ChessPiece m = k; k = null; f(); k = m; will temporarily store k in m, delete k, and then restore k.

Which ArrayList function is used to combine two ArrayLists?

Answer explanation

ArrayList<Object>.addAll() will add all elements of one ArrayList to another, which is the same as combining them.

In Java, what type is used to store a list of named constants, such as States?