我想通过输入字符串来计算平方根。我尝试使用Math.sqrt（字符串），但它不起作用。你知道怎么计算这个吗？
我真的不知道如何在这个库中使用它。
public class MainActivity extends ActionBarActivity {
// IDs of all the numeric buttons
private int[] numericButtons = {R.id.btnZero, R.id.btnOne, R.id.btnTwo, R.id.btnThree, R.id.btnFour, R.id.btnFive, R.id.btnSix, R.id.btnSeven, R.id.btnEight, R.id.btnNine};
// IDs of all the operator buttons
private int[] operatorButtons = {R.id.btnAdd, R.id.btnSubtract, R.id.btnMultiply, R.id.btnDivide,R.id.buttonSqr,R.id.tan,R.id.cos,
R.id.sin,R.id.open_bracket,R.id.close_bracket};
// TextView used to display the output
private EditText txtScreen;
// Represent whether the lastly pressed key is numeric or not
private boolean lastNumeric=true;
// Represent that current state is in error or not
private boolean stateError;
// If true, do not allow to add another DOT
private boolean lastDot;
private boolean firstTime = true;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Find the TextView
this.txtScreen = (EditText) findViewById(R.id.txtScreen);
// Find and set OnClickListener to numeric buttons
setNumericOnClickListener();
// Find and set OnClickListener to operator buttons, equal button and decimal point button
setOperatorOnClickListener();
}
//Find and set OnClickListener to numeric buttons.
private void setNumericOnClickListener() {
// Create a common OnClickListener
View.OnClickListener listener = new View.OnClickListener() {
@Override
public void onClick(View v) {
// Just append/set the text of clicked button
Button button = (Button) v;
if (stateError) {
// If current state is Error, replace the error message
txtScreen.setText(button.getText());
stateError = false;
} else {
// If not, already there is a valid expression so append to it
txtScreen.append(button.getText());
}
// Set the flag
lastNumeric = true;
firstTime = true;
}
};
// Assign the listener to all the numeric buttons
for (int id : numericButtons) {
findViewById(id).setOnClickListener(listener);
}
}
//Find and set OnClickListener to operator buttons, equal button and decimal point button.
private void setOperatorOnClickListener() {
// Create a common OnClickListener for operators
View.OnClickListener listener = new View.OnClickListener() {
@Override
public void onClick(View v) {
// If the current state is Error do not append the operator
// If the last input is number only, append the operator
if (lastNumeric && !stateError) {
Button button = (Button) v;
txtScreen.append(button.getText());
Log.d("dsfds",txtScreen.getText().toString());
lastNumeric = false;
lastDot = false; // Reset the DOT flag
firstTime = true;
}
}
};
// Assign the listener to all the operator buttons
for (int id : operatorButtons) {
findViewById(id).setOnClickListener(listener);
}
// Decimal point
findViewById(R.id.btnDot).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (lastNumeric && !stateError && !lastDot) {
txtScreen.append(".");
lastNumeric = false;
lastDot = true;
//firstTime = false;
}
}
});
//delete
findViewById(R.id.btndel).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (txtScreen.getText().toString().length() > 1) {
//remove string
String screen_new = txtScreen.getText().toString().substring(0, txtScreen.getText().toString().length() - 1);
txtScreen.setText(screen_new);
} else {
txtScreen.setText("");
}
lastNumeric = false;
stateError = false;
lastDot = false;
//firstTime = false;
}
});
// Clear button
findViewById(R.id.btnClear).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
txtScreen.setText(""); // Clear the screen
// Reset all the states and flags
lastNumeric = false;
stateError = false;
lastDot = false;
//firstTime = false;
}
});
// Equal button
findViewById(R.id.btnEqual).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
onEqual();
}
});
}
//Logic to calculate the solution
private void onEqual() {
// If the current state is error, nothing to do.
// If the last input is a number only, solution can be found.
//if (lastNumeric && !stateError) {
if ((firstTime || lastNumeric) && !stateError){
// Read the expression
String txt = txtScreen.getText().toString();
Log.d( txt, "error");
txt = txt.replaceAll("x", "*").replaceAll("÷", "/");
// Create an Expression (A class from exp4j library)
Expression expression = new ExpressionBuilder(txt).build();
try {
// Calculate the result and display
double result = expression.evaluate();
txtScreen.setText(Double.toString(result));
lastDot = true; // Result contains a dot
} catch (ArithmeticException ex) {
// Display an error message
txtScreen.setText("Error");
stateError = true;
lastNumeric = false;
}
}
}
}
答案 0 :(得分：0)
首先使用String对象将DecimalFormat转换为数字，然后使用parse函数计算平方根。
DecimalFormat df=new DecimalFormat(); sq=java.lang.Math.sqrt(df.parse(myString).doubleValue());