Eric Roberts Handout #11ACS 106A January 8, 2010Solutions to the Lecture Problems1. PutBeeperLine/* * File: PutBeeperLine.java * ------------------------ * This program tests the putBeeperLine method, which creates a * line of beepers moving forward from Karels position. */import stanford.karel.*;public class PutBeeperLine extends SuperKarel {public void run() {putBeeperLine();turnLeft();putBeeperLine();}/* * Creates a line of beepers by putting a beeper down on every * intersection between Karel's current position and the next wall. */private void putBeeperLine() {while (frontIsClear()) {putBeeper();move();}putBeeper();}}– 2 –2. BanishWinter/* * File: BanishWinter.java * ----------------------- * The BanishWinter subclass gets Karel adorn a series * of trees with a cluster of beeper leaves. */import stanford.karel.*;public class BanishWinter extends SuperKarel {/* Main program */public void run() {while (beepersInBag()) {findTree();addLeavesToTree();}moveToWall();}/* * Moves Karel up to the next tree. * * Programming style note: Since a tree is simply a wall, * this method can simply call moveToWall. You could * therefore replace the findTree call in the main program * with moveToWall, but the program might then be harder to * read because it violates the "tree" metaphor used at the * level of the main program. */private void findTree() {moveToWall();}/* * Adorns a single tree with a cluster of leaves. The * precondition is that Karel must be immediately * west of the tree, facing east; the postcondition is * that Karel is at the bottom of the other side of the * tree, facing east. */private void addLeavesToTree() {turnLeft();climbTree();addLeaves();descendToGround();turnLeft();}– 3 –/* * Climbs to the top of the tree. */private void climbTree() {while (rightIsBlocked()) {move();}}/* * Moves Karel back to the ground. Both the pre- and * postconditions have Karel facing south. */private void descendToGround() {moveToWall();}/* * Creates the cluster of leaves at the top of a tree. * The precondition is that Karel must be facing north at * the top of the tree; the postcondition is that Karel * is still at the top, but on the other side of the * trunk, facing south. */private void addLeaves() {turnRight();createBeeperSquare();move();turnRight();}/* * Moves Karel forward until it is blocked by a wall. */private void moveToWall() {while (frontIsClear()) {move();}}/* * Creates a square of four beepers, leaving Karel in its * original orientation. The resulting square is positioned * ahead and to the left of Karel's starting position. */private void createBeeperSquare() {for (int i = 0; i < 4; i++)
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