我有一个简单的搜索方法来比较用户的输入String和ArrayList中的String。当我使用input.nextLine（）时，它没有找到String，但是，当我使用input.next（）时，它工作正常。有人能解释为什么会出现这种错误吗
searchPlants方法是问题发生的地方。
司机：
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Scanner;
public class Driver {
public String ID = new String();
public String name = new String();
public String color = new String();
public String smell = new String();
public String hasThorns = new String();
public String isPoisonous = new String();
public String isMedicine = new String();
public String isEdible = new String();
Scanner input = new Scanner(System.in);
public static void main(String[] args) {new Driver();}
public Driver() {
ArrayList<Plant> plantPack = new ArrayList<>();
System.out.println("Welcome to the PlantPack Application.");
System.out.println("Please select a number from the options below.");
System.out.println("");
while (true) {
System.out.println("1: Add a plant to the pack.");
System.out.println("2: Remove a plant from the pack.");
System.out.println("3: Search for a specific plant.");
System.out.println("4: Display your plant pack.");
System.out.println("5: Filter the plant pack by incomplete name.");
System.out.println("0: Exit the plant pack interface.");
// Get the user input
int userChoice = input.nextInt();
switch (userChoice) {
case 1:
typeSwitch(plantPack);
break;
case 2:
removePlant(plantPack);
break;
case 3:
searchPlants(plantPack);
break;
case 4:
displayPlants(plantPack);
break;
case 5:
filterPlants(plantPack);
break;
case 0:
exitInterface();
break;
default:
System.out.println("Invalid entry. \nPlease choose between 1-5, or 0: ");
break;
}
}
}
public void typeSwitch(ArrayList<Plant> plantPack) {
System.out.println("Please enter what type of plant you are adding: ");
System.out.println("1: Flower");
System.out.println("2: Fungus");
System.out.println("3: Weed");
int type = input.nextInt();
if (type >= 1 && type <= 3) {
switch (type) {
case 1:
addFlower(plantPack);
break;
case 2:
addFungus(plantPack);
break;
case 3:
addWeed(plantPack);
break;
}
}
else
{
System.out.println("Invalid Entry. Please choose between 1-3: ");
typeSwitch(plantPack);
}
}
private void addFlower(ArrayList<Plant> plantPack) {
Flower newFlower = new Flower(ID, name, color, smell, hasThorns, isEdible, isPoisonous, isMedicine);
if(plantPack.size() < 25)
{
System.out.println("Enter a unique ID number for the flower you wish to add (E.g. F1, F2, etc): ");
newFlower.setID(input.next().trim());
input.nextLine(); //Scanner was eating first input for some reason. Had to fire a blank nextLine() to allow input for every entry, as seen in each subsequent method.
System.out.println("Enter the name of the flower you wish to add: ");
newFlower.setName(input.nextLine().trim());
System.out.println("Enter the color of the flower you wish to add: ");
newFlower.setColor(input.nextLine().trim());
System.out.println("Does the flower have a scent? Yes or No: ");
newFlower.setSmell(input.nextLine().trim());
System.out.println("Does the flower have thorns? Yes or No: ");
newFlower.setThorns(input.nextLine().trim());
System.out.println("Flower successfully added.\n ");
plantPack.add(newFlower);
}
else
{
System.out.println("You may only hold 25 items in your PlantPack. Please remove an item before adding another.\n");
}
}
private void addFungus(ArrayList<Plant> plantPack) {
Fungus newFungus = new Fungus(ID, name, color, smell, hasThorns, isEdible, isPoisonous, isMedicine);//(ID, name, color, isPoisonous);
if(plantPack.size() < 25)
{
System.out.println("Enter a unique ID number for the Fungus you wish to add (E.g. Fn1, Fn2, etc): ");
newFungus.setID(input.next().trim());
input.nextLine();
System.out.println("Enter the name of the Fungus you wish to add: ");
newFungus.setName(input.nextLine().trim());
System.out.println("Enter the color of the Fungus you wish to add: ");
newFungus.setColor(input.nextLine().trim());
System.out.println("Is this particular Fungus poisonous? Yes or No: ");
newFungus.setIsPoisonous(input.nextLine().trim());
System.out.println("Fungus successfully added.\n");
plantPack.add(newFungus);
}
else
{
System.out.println("You may only hold 25 items in your plant pack. Please remove one before adding another.");
}
}
private void addWeed(ArrayList<Plant> plantPack) {
Weed newWeed = new Weed(ID, name, color, smell, hasThorns, isEdible, isPoisonous, isMedicine); //(ID, name, color, isEdible, isPoisonous);
if(plantPack.size() < 25)
{
System.out.println("Enter a unique ID number for the Weed you wish to add (E.g. W1, W2, etc): ");
newWeed.setID(input.next().trim());
input.nextLine();
System.out.println("Enter the name of the Weed you wish to add: ");
newWeed.setName(input.nextLine().trim());
System.out.println("Enter the color of the Weed you wish to add: ");
newWeed.setColor(input.nextLine().trim());
System.out.println("Is this particular Weed edible? Yes or No: ");
newWeed.setIsEdible(input.nextLine().trim());
System.out.println("Is this particular Weed medicinal? Yes or No: ");
newWeed.setIsMedicine(input.nextLine().trim());
System.out.println("Weed successfully added.\n");
plantPack.add(newWeed);
}
else
{
System.out.println("You may only hold 25 items in your plant pack. Please remove one before adding another.");
}
}
private void removePlant(ArrayList<Plant> plantPack) {
System.out.println("Which type of Plant do you wish to remove?");
System.out.println("1: Flower");
System.out.println("2: Fungus");
System.out.println("3: Weed");
int type = input.nextInt();
switch (type) {
case 1:
System.out.println("Enter the ID number of the Flower you want to remove: ");
String deleteFlowerID = input.next().trim();
input.nextLine();
System.out.println("Enter the name of the Flower you wish to remove: ");
String deleteName = input.nextLine().trim();
boolean found = false;
Iterator<Plant> itr = plantPack.iterator(); //a basic for loop and .equals() would not work, and I don't understand why. I had to go with an Iterator.
while(itr.hasNext()) {
Plant flowers = itr.next();
if(flowers.getID().equals(deleteFlowerID) && flowers.getName().equals(deleteName)) {
itr.remove();
found = true;
break;
}
}
if (found)
{
System.out.println("That Flower was successfully removed from your inventory.");
}
else
{
System.out.println("That Flower was not found in your inventory.");
}
break;
case 2:
System.out.println("Enter the ID number of the Fungus you want to remove: ");
String deleteFungusID = input.next().trim();
input.nextLine();
System.out.println("Enter the name of the Fungus you wish to remove: ");
String deleteFungusName = input.nextLine().trim();
boolean foundFungus = false;
Iterator<Plant> fungusItr = plantPack.iterator();
while(fungusItr.hasNext()) {
Plant fungi = fungusItr.next();
if(fungi.getID().equals(deleteFungusID) && fungi.getName().equals(deleteFungusName)) {
fungusItr.remove();
foundFungus = true;
break;
}
}
if (foundFungus)
{
System.out.println("That Fungus was successfully removed from your inventory.");
}
else
{
System.out.println("That Fungus was not found in your inventory.");
}
break;
case 3:
System.out.println("Enter the ID number of the Weed you want to remove: ");
String deleteWeedID = input.next().trim();
input.nextLine();
System.out.println("Enter the name of the Weed you wish to remove: ");
String deleteWeedName = input.nextLine().trim();
boolean foundWeed = false;
Iterator<Plant> weedItr = plantPack.iterator();
while(weedItr.hasNext()) {
Plant weeds = weedItr.next();
if(weeds.getID().equals(deleteWeedID) && weeds.getName().equals(deleteWeedName)) {
weedItr.remove();
foundWeed = true;
break;
}
}
if (foundWeed)
{
System.out.println("That Weed was successfully removed from your inventory.");
}
else
{
System.out.println("That Weed was not found in your inventory.");
}
break;
}
}
private void searchPlants(ArrayList<Plant> plantPack) {
System.out.println("Please enter the ID of the plant you're searching for: ");
String searchID = input.next().trim();
input.nextLine();
boolean match = false;
for(int i = 0; i < plantPack.size(); i++) {
if(plantPack.get(i).getID().equals(searchID))
{
match = true;
break;
}
}
if(match)
{
System.out.println("Found that one in your PlantPack!");
}
else
{
System.out.println("Sorry, did not find that one.");
}
}
private void displayPlants(ArrayList<Plant> plantPack) {
for(Plant plants : plantPack) {
System.out.println(plants);
}
}
private void filterPlants(ArrayList<Plant> plantPack) {
}
private void exitInterface() {
System.out.println("Are you sure you want to exit the PlantPack Application? Y or N: ");
while(true) {
String answer = input.next();
if(!"Y".equalsIgnoreCase(answer) && !"N".equalsIgnoreCase(answer))
{
System.out.println("Please enter Y or N (not case-sensitive): ");
}
if("Y".equalsIgnoreCase(answer))
{
System.out.println("Thank you for using the PlantPack Application. See ya later!");
System.exit(0);
}
if("N".equalsIgnoreCase(answer))
{
break;
}
}
}
}
植物类：
public class Plant {
public String ID;
public String name;
public String color;
public String smell;
public String hasThorns;
public String isEdible;
public String isPoisonous;
public String isMedicine;
public Plant(String ID, String name, String color, String smell, String hasThorns, String isEdible, String isPoisonous, String isMedicine) {
this.ID = ID;
this.name = name;
this.color = color;
this.smell = smell;
this.hasThorns = hasThorns;
this.isEdible = isEdible;
this.isPoisonous = isPoisonous;
this.isMedicine = isMedicine;
}
public void setColor(String color) {this.color = color;}
public void setID(String ID) {this.ID = ID;}
public void setName(String name) {this.name = name;}
public String getID() {return ID;}
public String getName() {return name;}
public String getColor() {
return color;
}
public String toString() {
return "ID: " + this.ID + ", Name: " + this.name + ", Color " + this.color;
}
}
和花班：
public class Flower extends Plant {
public Flower(String ID, String name, String color, String smell, String hasThorns, String isEdible, String isPoisonous, String isMedicine) {
super(ID, name, color, smell, hasThorns, isEdible, isPoisonous, isMedicine);
}
public void setSmell(String smell) {this.smell = smell;}
public void setThorns(String hasThorns) {
this.hasThorns = hasThorns;
}
public String getSmell() {
return smell;
}
public String getHasThorns() {
return hasThorns;
}
public String toString() {
return super.toString() + ", Scent? " + this.smell + ", Thorns? " + this.hasThorns;
}
}
这是使用input.nextLine（）时的输出：
Welcome to the PlantPack Application.
Please select a number from the options below.
1: Add a plant to the pack.
2: Remove a plant from the pack.
3: Search for a specific plant.
4: Display your plant pack.
5: Filter the plant pack by incomplete name.
0: Exit the plant pack interface.
1
Please enter what type of plant you are adding:
1: Flower
2: Fungus
3: Weed
1
Enter a unique ID number for the flower you wish to add (E.g. F1, F2, etc):
F1
Enter the name of the flower you wish to add:
rose
Enter the color of the flower you wish to add:
red
Does the flower have a scent? Yes or No:
yes
Does the flower have thorns? Yes or No:
yes
Flower successfully added.
1: Add a plant to the pack.
2: Remove a plant from the pack.
3: Search for a specific plant.
4: Display your plant pack.
5: Filter the plant pack by incomplete name.
0: Exit the plant pack interface.
4
ID: F1, Name: rose, Color red, Scent? yes, Thorns? yes
1: Add a plant to the pack.
2: Remove a plant from the pack.
3: Search for a specific plant.
4: Display your plant pack.
5: Filter the plant pack by incomplete name.
0: Exit the plant pack interface.
3
Please enter the ID of the plant you're searching for:
F1
Sorry, did not find that one.
现在，同样的事情，但改为使用input.next（）：
Please enter the ID of the plant you're searching for:
F1
Found that one in your PlantPack!
答案 0 :(得分：1)
程序“吃掉”你的新系列。这将导致程序跳过一行。
如果您输入： input.nextLine（）; input.nextLine（）; （两倍）
它应该有用