我想创建一个简单的二次方程求解器，但是当我运行它时，它会被捕获到每个按钮的第一个if语句。有什么想法吗？
public class MainActivity extends AppCompatActivity {
Button button1, button2;
String a_temp;
EditText b_temp;
EditText c_temp;
TextView tv1, tv2;
Double a,b,c;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG).setAction("Action", null).show();
}
});
a_temp = ((EditText)findViewById(R.id.editText)).getText().toString();
if (a_temp.equals("")) {
a = Double.valueOf(0);
} else {
a = Double.valueOf(a_temp);
}
b_temp = (EditText)findViewById(R.id.editText2);
if (!b_temp.getText().toString().equals("")) {
b = Double.parseDouble(b_temp.getText().toString());
}else {
b = Double.valueOf(0);
}
c_temp = (EditText)findViewById(R.id.editText3);
if (!c_temp.getText().toString().equals("")) {
c = Double.parseDouble(c_temp.getText().toString());
}else {
c = Double.valueOf(0);
}
tv1 = (TextView) findViewById(R.id.textView2);
tv2 = (TextView) findViewById(R.id.textView3);
button1 = (Button) findViewById(R.id.button);
button2 = (Button) findViewById(R.id.button2);
button1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if (a == 0) {
tv1.setText("That's not a quadratic equation");
}else {
if (b*b - 4*a*c < 0) {
tv1.setText("This quadratic equation has no real roots");
} else {
double root1 = (-b + Math.sqrt(Math.pow(b,2) - 4 * a * c))/(2*a);
double root2 = (-b - Math.sqrt(Math.pow(b,2) - 4 * a * c))/(2*a);
double result = Math.max(root1,root2);
tv1.setText(String.valueOf(result));
}
}
}
});
button2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if (a == 0) {
tv2.setText("That's not a quadratic equation");
}else {
if (b * b - 4 * a * c < 0) {
tv2.setText("This quadratic equation has no real roots");
} else {
double root1 = (-b + Math.sqrt(Math.pow(b, 2) - 4 * a * c)) / (2 * a);
double root2 = (-b - Math.sqrt(Math.pow(b, 2) - 4 * a * c)) / (2 * a);
double result = Math.min(root1, root2);
tv2.setText(" " + result);
}
}
};
});
}
XML代码：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Type the operands of the quadratic equation you want to solve"
android:id="@+id/textView"
android:layout_marginTop="39dp"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Root #1"
android:id="@+id/button"
android:layout_marginTop="60dp"
android:layout_below="@+id/editText3"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Root #2"
android:id="@+id/button2"
android:layout_marginTop="69dp"
android:layout_alignTop="@+id/button"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:id="@+id/textView2"
android:layout_alignBottom="@+id/button"
android:layout_alignTop="@+id/button"
android:layout_alignRight="@+id/textView"
android:layout_alignEnd="@+id/textView"
android:layout_toRightOf="@+id/button"
android:layout_toEndOf="@+id/button"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="false" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceMedium"
android:id="@+id/textView3"
android:layout_alignBottom="@+id/button2"
android:layout_toRightOf="@+id/button2"
android:layout_alignTop="@+id/button2"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number|numberSigned"
android:ems="10"
android:id="@+id/editText"
android:layout_marginTop="32dp"
android:layout_below="@+id/textView"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_toLeftOf="@+id/textView2"
android:layout_toStartOf="@+id/textView2" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number|numberSigned"
android:ems="10"
android:id="@+id/editText2"
android:layout_below="@+id/editText"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_toLeftOf="@+id/textView2"
android:layout_toStartOf="@+id/textView2" />
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="number|numberSigned"
android:ems="10"
android:id="@+id/editText3"
android:layout_below="@+id/editText2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_toLeftOf="@+id/textView2"
android:layout_toStartOf="@+id/textView2" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="x^2"
android:id="@+id/textView4"
android:layout_alignTop="@+id/editText"
android:layout_alignLeft="@+id/textView2"
android:layout_alignStart="@+id/textView2" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="x"
android:id="@+id/textView5"
android:layout_below="@+id/editText"
android:layout_alignLeft="@+id/textView4"
android:layout_alignStart="@+id/textView4" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="=0"
android:id="@+id/textView6"
android:layout_alignBottom="@+id/editText3"
android:layout_alignLeft="@+id/textView5"
android:layout_alignStart="@+id/textView5" />
</RelativeLayout>
答案 0 :(得分：0)
您正在将双倍值与==进行比较。
问题是它可能不等于0，因为存储双值时存在轻微错误。例如，它将类似于0.000000001或-0.00000001。相反，比较如下：
if (Math.abs(a) < 0.0000001) { ... }
你忘了按2 * a划分你的根。
答案 1 :(得分：0)
因此，我看到的主要问题是，您要在活动类的a方法中为b，c和onCreate分配值。
这意味着，只要您的活动被创建，即在用户有时间将任何数据输入您的EditText字段之前，您就会尝试读取所述不存在的输入 - 即{{1} }。
这就是为什么在每个0方法中，检查零值的第一个onClick子句返回true。因为值为零。
你应该做的是移动每个变量的这一部分：
if()进入 if (!c_temp.getText().toString().equals("")) {
c = Double.parseDouble(c_temp.getText().toString());
}else {
c = Double.valueOf(0);
}
类，即进入OnClickListener方法，根据当前用户输入“刷新”您在计算中使用的值。