我有2个名单 -
[（Tandoor，Indian），（Biryani，Indian），（比萨，意大利）]
{在上面，左边的项目是右边的美食类型的食品}
和
[（John，Indian），（Mary，Indian），（Sam，Italian）]
{在上面，左边的人可以选择正确的菜肴类型}
我需要打印出列表的内容为 约翰坦多尔 约翰·比亚尼 玛丽坦多尔 玛丽·比亚尼 Sam Pizza
用于初始化2个给定列表，打印输出和处理Pair对象（比较，访问键和值）的API。
为什么我会在以下内容中获得nullpointerexception -
package a1;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Scanner;
public class main {
static class Pair implements Comparable<Pair>{
String pairKey;
String pairValue;
Pair(String pairKey, String pairValue) {
this.pairKey = pairKey;
this.pairValue = pairValue;
}
public String getPairKey() {
return pairKey;
}
public String getPairValue() {
return pairValue;
}
public String toString() {
return getPairKey() + " " + getPairValue();
}
@Override
public int compareTo(Pair pair) {
int compare = pairKey.compareTo(pair.getPairKey());
if(compare == 0) {
compare = pairValue.compareTo(pair.getPairValue());
}
return compare;
}
}
static List<Pair> solve(List<Pair> lunchMenuPairs, List<Pair> teamCuisinePreferencePairs){
List<Pair> result= null;
for(Pair first : teamCuisinePreferencePairs){
for(Pair name : lunchMenuPairs)
{
String a1 = first.getPairValue();
String a2 = name.getPairValue();
String a3 = first.getPairKey();
String a4 = name.getPairKey();
if(first.compareTo(name)==0)
{
System.out.println(a3);
System.out.println(a4);
Pair pair = new Pair(a3,a4);
result.add(pair);
}
}
}
return result;
}
private static void readAndSetParameters(List<Pair> lunchMenuPairs, List<Pair> teamCuisinePreferencePairs) {
int lunchMenuPairCount = -1;
int teamCuisinePreferencePairCount = -1;
String tempOption = null, tempOptionValue = null;;
try(Scanner in = new Scanner(System.in)) {
lunchMenuPairCount = in.nextInt();
while(lunchMenuPairCount > 0) {
lunchMenuPairCount--;
tempOption = in.next();
tempOptionValue = in.next();
Pair pair = new Pair(tempOption, tempOptionValue);
lunchMenuPairs.add(pair);
}
teamCuisinePreferencePairCount = in.nextInt();
while(teamCuisinePreferencePairCount > 0) {
teamCuisinePreferencePairCount--;
tempOption = in.next();
tempOptionValue = in.next();
Pair pair = new Pair(tempOption, tempOptionValue);
teamCuisinePreferencePairs.add(pair);
}
}
}
private static void print(List<?> resultPairs) {
for (Object pair : resultPairs) {
System.out.println(pair);
}
}
public static void main(String[] args){
List<Pair> lunchMenuPairs = new LinkedList<>();
List<Pair> teamCuisinePreferencePairs = new LinkedList<>();
readAndSetParameters(lunchMenuPairs, teamCuisinePreferencePairs);
List<Pair> result = solve( lunchMenuPairs, teamCuisinePreferencePairs );
Collections.sort(result);
print(result);
}
}
答案 0 :(得分：1)
更改
import { Component } from '@angular/core';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
import { NavController, AlertController, ToastController, ViewController, Events, LoadingController } from 'ionic-angular';
import { WelcomePage } from '../welcome/welcome';
import { PmsServiceProvider } from '../../providers/pms-service/pms-service';
@Component({
selector: 'page-home',
templateUrl: 'home.html'
})
export class HomePage {
public emailError: boolean = false;
public passwordError: boolean = false;
userForm: FormGroup;
public loginStatus: boolean = true;
public rememberChecked = true;
Email;
Password3;
check;
logined : boolean =false;
checkStatus=1;
toast = this.toastCtrl.create({
message: 'Please enter correct email Id and password',
duration: 3000,
position: 'bottom'
})
public loading = this.loadingCtrl.create({
content: 'Loading...',
spinner: 'bubbles'
});
constructor(public navCtrl: NavController, private form: FormBuilder, private alertCtrl: AlertController, private toastCtrl: ToastController, private service: PmsServiceProvider, public viewCtrl : ViewController, public events: Events, public loadingCtrl: LoadingController) {
console.log("in constructor");
events.subscribe('user:created', (data)=>{
this.Email=localStorage.getItem("email");
this.Password3=localStorage.getItem("password");
})
this.userForm = form.group({
email: [null, [Validators.required]],
password: [null, [Validators.required]]
})
}
login(inputForm) {
console.log(inputForm.value.email);
console.log(inputForm.value.password);
if (inputForm.value.email == null || inputForm.value.email == "") {
this.emailError = true;
} else {
this.emailError = false;
}
if (inputForm.value.password == null || inputForm.value.password == "") {
this.passwordError = true;
} else {
this.passwordError = false;
}
if (inputForm.value.email == null || inputForm.value.password == null || inputForm.value.email == "" || inputForm.value.password == "") {
console.log("one is null");
this.loginStatus = false;
}
else {
this.loginStatus = true;
}
//CODE FOR TESTING THE EMAIL ID AND PASSWORD IS CORRECT
// Hit to the Api.
if (this.loginStatus == true) {
this.loading.present().then(()=>{
this.service.checkUser(inputForm.value).subscribe(resData => {
// console.log(resData.data.body);
console.log(resData);
if(this.loading){
this.loading.dismiss();
// this.loading =null;
}
// console.log(resData.success);
// console.log(resData.body[0]);
if (resData.success == true) {
if(this.rememberChecked ==true){
localStorage.setItem("email",inputForm.value.email);
localStorage.setItem("password",inputForm.value.password);
localStorage.setItem("user_id",resData.data.body[0].id);
}else{
localStorage.setItem("email","");
localStorage.setItem("password","");
}
// console.log(resData.respData[0].id);
localStorage.setItem("token",resData.data.mytoken);
console.log(resData.data.body[0].first_name);
this.navCtrl.push(WelcomePage, { id: resData.data.body[0].id, name : resData.data.body[0].first_name}).then(()=>{
const index = this.navCtrl.getActive().index;
this.navCtrl.remove(0,index);
});
// this.navCtrl.setRoot(WelcomePage);
}
else {
this.toast.present();;
}
})
});
;
}
}
}
到
static List<Pair> solve(List<Pair> lunchMenuPairs, List<Pair> teamCuisinePreferencePairs){
List<Pair> result= null;
...