java.lang.NumberFormatException：无效的int：“”Vogella Dijkstra算法

Question

我想使用来自Dijkstra shortest path algorithm的 Vogella Dijkstra算法来生成最短路径并绘制路径。

Android Studio不会出现任何语法错误，但是当我启动我的应用时，它会说“不幸的是，DijkstraAlgorithmTest已停止”

我将在下面发布所有代码以及Logcat：

MainActivity.java

package com.example.lyeji.dijkstraalgorithmtest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
private List<Vertex> nodes;
private List<Edge> edges;
private static String tempPath ="";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    nodes = new ArrayList<Vertex>();
    edges = new ArrayList<Edge>();
    for (int i = 0; i < 11; i++) {
        Vertex location = new Vertex("Node_" + i, "" + i);
        nodes.add(location);
    }

    addLane("Edge_0", 0, 1, 85);
    addLane("Edge_1", 0, 2, 217);
    addLane("Edge_2", 0, 4, 173);
    addLane("Edge_3", 2, 6, 186);
    addLane("Edge_4", 2, 7, 103);
    addLane("Edge_5", 3, 7, 183);
    addLane("Edge_6", 5, 8, 250);
    addLane("Edge_7", 8, 9, 84);
    addLane("Edge_8", 7, 9, 167);
    addLane("Edge_9", 4, 9, 502);
    addLane("Edge_10", 9, 10, 40);
    addLane("Edge_11", 1, 10, 600);

    // Lets check from location Loc_1 to Loc_10
    Graph graph = new Graph(nodes, edges);
    DijkstraAlgorithm dijkstra = new DijkstraAlgorithm(graph);
    dijkstra.execute(nodes.get(0));
    LinkedList<Vertex> path = dijkstra.getPath(nodes.get(10));

    //assertNotNull(path);
    //assertTrue(path.size() > 0);

    String temp = "";

    for (Vertex vertex : path)
    {
        temp += vertex + " ";
    }

    if (temp !=null && temp.length()>0 && temp.charAt(temp.length()-1) == 'x')
    {
        temp = temp.substring(0,temp.length()-1);
    }


    temp = removeLastChar(temp);
    tempPath = temp;


}

private void addLane(String laneId, int sourceLocNo, int destLocNo,
                     int duration) {
    Edge lane = new Edge(laneId,nodes.get(sourceLocNo), nodes.get(destLocNo), duration );
    edges.add(lane);
}

private static String removeLastChar(String str)
{
    return str.substring(0, str.length()-1);
}


public static String getPath()
{

    return tempPath;
}
}

Navigation.java

package com.example.lyeji.dijkstraalgorithmtest;

import android.content.Context;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

/**
 * Created by lyeji on 08-Mar-18.
 */

public class Navigation extends View {

Paint paint;
static Path path , path2;


static String temp = MainActivity.getPath();
int [] pathTaken;

float[] xcoor = {260,260,115,260,40,260,230,440,440,630,730,730,730,730,490};
float[] ycoor = {1035,860,860,715,715,585,400,585,345,585,585,685,940,1035,1035};

public Navigation (Context context){

  super(context);
  initialrun();
  init();
}

public Navigation (Context context, AttributeSet attrs){

    super(context,attrs);
    initialrun();
    init();
}

public void initialrun(){

    String items = "";
    String[] tempPath ;
    items = temp.replaceAll(" ", ",");
    tempPath = items.split(",");
    pathTaken = new int[tempPath.length];

    for (int i = 0; i < tempPath.length; i++) {

        pathTaken[i] = Integer.parseInt(tempPath[i]);

    }


    for (int i = 0; i < tempPath.length; i++) {
       tempPath[i] = null;

    }
}

public Navigation (Context context, AttributeSet attrs,int defStyle){

    super(context,attrs,defStyle);
    initialrun();
    init();
}

private void init(){

    paint = new Paint();
    paint.setColor(Color.BLUE);
    paint.setStrokeWidth(10);
    paint.setStyle(Paint.Style.STROKE);

    path = new Path();
    path2 = new Path();

    path.moveTo(xcoor[pathTaken[0]],ycoor[pathTaken[0]]);

    for(int i=1;i<pathTaken.length;i++){

        float a = xcoor[pathTaken[i]];
        float b = ycoor[pathTaken[i]];
        path.lineTo(a,b);


    }

}
}

DijkstraAlgorithm.java

package com.example.lyeji.dijkstraalgorithmtest;

/**
 * Created by lyeji on 04-Mar-18.
 */

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class DijkstraAlgorithm {

private final List<Vertex> nodes;
private final List<Edge> edges;
private Set<Vertex> settledNodes;
private Set<Vertex> unSettledNodes;
private Map<Vertex, Vertex> predecessors;
private Map<Vertex, Integer> distance;

public DijkstraAlgorithm(Graph graph) {
    // create a copy of the array so that we can operate on this array
    this.nodes = new ArrayList<Vertex>(graph.getVertexes());
    this.edges = new ArrayList<Edge>(graph.getEdges());
}

public void execute(Vertex source) {
    settledNodes = new HashSet<Vertex>();
    unSettledNodes = new HashSet<Vertex>();
    distance = new HashMap<Vertex, Integer>();
    predecessors = new HashMap<Vertex, Vertex>();
    distance.put(source, 0);
    unSettledNodes.add(source);
    while (unSettledNodes.size() > 0) {
        Vertex node = getMinimum(unSettledNodes);
        settledNodes.add(node);
        unSettledNodes.remove(node);
        findMinimalDistances(node);
    }
}

private void findMinimalDistances(Vertex node) {
    List<Vertex> adjacentNodes = getNeighbors(node);
    for (Vertex target : adjacentNodes) {
        if (getShortestDistance(target) > getShortestDistance(node)
                + getDistance(node, target)) {
            distance.put(target, getShortestDistance(node)
                    + getDistance(node, target));
            predecessors.put(target, node);
            unSettledNodes.add(target);
        }
    }

}

private int getDistance(Vertex node, Vertex target) {
    for (Edge edge : edges) {
        if (edge.getSource().equals(node)
                && edge.getDestination().equals(target)) {
            return edge.getWeight();
        }
    }
    throw new RuntimeException("Should not happen");
}

private List<Vertex> getNeighbors(Vertex node) {
    List<Vertex> neighbors = new ArrayList<Vertex>();
    for (Edge edge : edges) {
        if (edge.getSource().equals(node)
                && !isSettled(edge.getDestination())) {
            neighbors.add(edge.getDestination());
        }
    }
    return neighbors;
}

private Vertex getMinimum(Set<Vertex> vertexes) {
    Vertex minimum = null;
    for (Vertex vertex : vertexes) {
        if (minimum == null) {
            minimum = vertex;
        } else {
            if (getShortestDistance(vertex) < getShortestDistance(minimum)) {
                minimum = vertex;
            }
        }
    }
    return minimum;
}

private boolean isSettled(Vertex vertex) {
    return settledNodes.contains(vertex);
}

private int getShortestDistance(Vertex destination) {
    Integer d = distance.get(destination);
    if (d == null) {
        return Integer.MAX_VALUE;
    } else {
        return d;
    }
}

/*
 * This method returns the path from the source to the selected target and
 * NULL if no path exists
 */
public LinkedList<Vertex> getPath(Vertex target) {
    LinkedList<Vertex> path = new LinkedList<Vertex>();
    Vertex step = target;
    // check if a path exists
    if (predecessors.get(step) == null) {
        return null;
    }
    path.add(step);
    while (predecessors.get(step) != null) {
        step = predecessors.get(step);
        path.add(step);
    }
    // Put it into the correct order
    Collections.reverse(path);
    return path;
}
}

顶点，边缘和图形代码与Dijkstra Shortest Path Algorithm

相同

XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="16dp"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:paddingTop="16dp"
android:orientation="vertical"
tools:context="com.example.lyeji.dijkstraalgorithmtest.MainActivity">

<com.example.lyeji.dijkstraalgorithmtest.Navigation
    android:layout_width="1100px"
    android:layout_height="1250px" />



</RelativeLayout>

logcat的

03-08 11:42:43.225 13819-13819/com.example.lyeji.dijkstraalgorithmtest E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.lyeji.dijkstraalgorithmtest, PID: 13819
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lyeji.dijkstraalgorithmtest/com.example.lyeji.dijkstraalgorithmtest.MainActivity}: android.view.InflateException: Binary XML file line #0: Binary XML file line #0: Error inflating class com.example.lyeji.dijkstraalgorithmtest.Navigation
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2611)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2677)
 at android.app.ActivityThread.-wrap11(ActivityThread.java)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515)
 at android.os.Handler.dispatchMessage(Handler.java:111)
 at android.os.Looper.loop(Looper.java:227)
 at android.app.ActivityThread.main(ActivityThread.java:6100)
 at java.lang.reflect.Method.invoke(Native Method)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:859)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749)
Caused by: android.view.InflateException: Binary XML file line #0: Binary XML file line #0: Error inflating class com.example.lyeji.dijkstraalgorithmtest.Navigation
 at android.view.LayoutInflater.inflate(LayoutInflater.java:539)
 at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
 at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
 at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287)
 at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139)
 at com.example.lyeji.dijkstraalgorithmtest.MainActivity.onCreate(MainActivity.java:19)
 at android.app.Activity.performCreate(Activity.java:6280)
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1131)
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2564)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2677) 
 at android.app.ActivityThread.-wrap11(ActivityThread.java) 
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515) 
 at android.os.Handler.dispatchMessage(Handler.java:111) 
 at android.os.Looper.loop(Looper.java:227) 
 at android.app.ActivityThread.main(ActivityThread.java:6100) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:859) 
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749) 
Caused by: android.view.InflateException: Binary XML file line #0: Error inflating class com.example.lyeji.dijkstraalgorithmtest.Navigation
 at android.view.LayoutInflater.createView(LayoutInflater.java:645)
 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:764)
 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
 at android.view.LayoutInflater.rInflate(LayoutInflater.java:835)
 at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798)
 at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
 at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
 at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287) 
 at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
 at com.example.lyeji.dijkstraalgorithmtest.MainActivity.onCreate(MainActivity.java:19) 
 at android.app.Activity.performCreate(Activity.java:6280) 
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1131) 
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2564) 
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2677) 
 at android.app.ActivityThread.-wrap11(ActivityThread.java) 
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515) 
 at android.os.Handler.dispatchMessage(Handler.java:111) 
 at android.os.Looper.loop(Looper.java:227) 
 at android.app.ActivityThread.main(ActivityThread.java:6100) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:859) 
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749) 
Caused by: java.lang.reflect.InvocationTargetException
 at java.lang.reflect.Constructor.newInstance(Native Method)
 at android.view.LayoutInflater.createView(LayoutInflater.java:619)
 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:764) 
 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704) 
 at android.view.LayoutInflater.rInflate(LayoutInflater.java:835) 
 at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:515) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
 at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287) 
 at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
 at com.example.lyeji.dijkstraalgorithmtest.MainActivity.onCreate(MainActivity.java:19) 
 at android.app.Activity.performCreate(Activity.java:6280) 
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1131) 
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2564) 
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2677) 
 at android.app.ActivityThread.-wrap11(ActivityThread.java) 
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515) 
 at android.os.Handler.dispatchMessage(Handler.java:111) 
 at android.os.Looper.loop(Looper.java:227) 
 at android.app.ActivityThread.main(ActivityThread.java:6100) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:859) 
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749) 
Caused by: java.lang.NumberFormatException: Invalid int: ""
 at java.lang.Integer.invalidInt(Integer.java:138)
 at java.lang.Integer.parseInt(Integer.java:358)
 at java.lang.Integer.parseInt(Integer.java:334)
 at com.example.lyeji.dijkstraalgorithmtest.Navigation.initialrun(Navigation.java:51)
 at com.example.lyeji.dijkstraalgorithmtest.Navigation.<init>(Navigation.java:37)
 at java.lang.reflect.Constructor.newInstance(Native Method) 
 at android.view.LayoutInflater.createView(LayoutInflater.java:619) 
 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:764) 
 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704) 
 at android.view.LayoutInflater.rInflate(LayoutInflater.java:835) 
 at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:798) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:515) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:423) 
 at android.view.LayoutInflater.inflate(LayoutInflater.java:374) 
 at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:287) 
 at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139) 
 at com.example.lyeji.dijkstraalgorithmtest.MainActivity.onCreate(MainActivity.java:19) 
 at android.app.Activity.performCreate(Activity.java:6280) 
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1131) 
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2564) 
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2677) 
 at android.app.ActivityThread.-wrap11(ActivityThread.java) 
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515) 
 at android.os.Handler.dispatchMessage(Handler.java:111) 
 at android.os.Looper.loop(Looper.java:227) 
 at android.app.ActivityThread.main(ActivityThread.java:6100) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:859) 
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749) 

我认为主要问题来自Navigation.java:51

pathTaken[i] = Integer.parseInt(tempPath[i]);

我认为问题是它没有将任何int存储到pathTaken [i]中，但我无法找出为什么会出现此错误。

我已经面临这个问题好几个小时了。我希望有人可以帮我找出问题所在。提前谢谢！

Answer 1

尝试更改此行并检查tempPath中的所有字符串是否为空（可能根本没有分配tempPath）。

pathTaken[i] = Integer.parseInt(tempPath[i].isEmpty() ? 0 : tempPath[i]);