如何解决此错误java.lang.Object []无法转换为java.lang.String []？

Question

Im not to sure how to fix this since my code is String[] and not Object[] How would i go about fixing this error?

Here is s the full logcat:

06-14 00:25:40.356: W/dalvikvm(13023): threadid=1: thread exiting with uncaught exception (group=0x40aa41f8)
06-14 00:25:40.356: E/AndroidRuntime(13023): FATAL EXCEPTION: main
06-14 00:25:40.356: E/AndroidRuntime(13023): java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.String[]
06-14 00:25:40.356: E/AndroidRuntime(13023):    at com.example.drawingarrays.OutPutConversion.Out(OutPutConversion.java:7)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at com.example.drawingarrays.MainActivity.onClick(MainActivity.java:64)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at android.view.View.performClick(View.java:3540)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at android.view.View$PerformClick.run(View.java:14167)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at android.os.Handler.handleCallback(Handler.java:605)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at android.os.Looper.loop(Looper.java:137)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at android.app.ActivityThread.main(ActivityThread.java:4586)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at java.lang.reflect.Method.invokeNative(Native Method)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at java.lang.reflect.Method.invoke(Method.java:511)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-14 00:25:40.356: E/AndroidRuntime(13023):    at dalvik.system.NativeStart.main(Native Method)

Here is my code:

public class OutPutConversion {
DrawingTools GAL = new DrawingTools();

public void Out() {
    String[] Result = (String[]) GAL.getAL().toArray();
    float[] vertices = new float[Result.length];
    for (int i = 0; i < vertices.length; i++) {
        vertices[i] = Float.valueOf(Result[i]);

    }
  }
}

Here is the DrawingTools Class:

public class DrawingTools {
ArrayList<String> AL = new ArrayList<String>();

public ArrayList<String> getAL() {
    return AL;
}

public void AddLine(String Input1) {
    String[] pStrings = Input1.split(",");
    for (int i = 0; i < pStrings.length; i++) {
        AL.add(pStrings[i]);
    }

}

Answer 1

GAL.getAL（）返回ArrayList<String> ，但是ArrayList.toArray（）返回Object []的通用类型是什么（请参阅API），并且您不能将其GAL.getAL().toArray(new String[0])为String []，请尝试GAL.getAL().toArray(new String[0])改为使用GAL.getAL().toArray(new String[0])

Answer 2

You can not cast an entire array, so you have to convert it, or cast it inside the loop appropriately. Or in this case no cast at all.

public void Out() {
    Object[] Result = GAL.getAL().toArray();
    float[] vertices = new float[Result.length];
    for (int i = 0; i < vertices.length; i++) {
        vertices[i] = Float.valueOf(Result[i].toString());

    }
}

Answer 3

Arrays do not follow inheritance rules of their elements. The fact that String extends Object does not mean that String[] extends Object[] .

To "cast" from Object[] to String[] you have to create new string array, iterate over elements of object array and copy element-by element with casting exactly as you do this for float.

so, the simplest fix to your code is just do the following:

Object[] Result = GAL.getAL().toArray();
float[] vertices = new float[Result.length];
for (int i = 0; i < vertices.length; i++) {
    vertices[i] = Float.valueOf(String.valuOf(Result[i]));
}

However as far as I understand getAL() method returns Collection<String> . So, you can:

 String[] Result = GAL.getAL().toArray(new String[0]);
    float[] vertices = new float[Result.length];
    for (int i = 0; i < vertices.length; i++) {
        vertices[i] = Float.valueOf(Result[i]);
    }

or even just directly iterate the collection:

Collection<String> Result = GAL.getAL();
float[] vertices = new float[Result.size()];
for (int i = 0; i < vertices.length; i++) {
    vertices[i] = Float.valueOf(Result[i]);
}

And the last tip. There is naming convention in java. All variables and methods names start with small letter. All classes names start with capital letter. Start follow this convention now. Otherwise your code will be unreadable.