计算一个正确的字符串形式运算式(若要实现计算器，还需对表达式的合法性进行判断)
效果图
计算器效果图
运算代码CalculatorMathUtil.java
import java.math.BigDecimal;
import java.math.MathContext;
import java.util.Stack;
/**
* 计算一个正确的字符串形式运算式
* @author HLP
*
*/
public class CalculatorMathUtil {
/**
* 数据栈
*/
Stack number;
/**
* 符号栈
*/
Stack operator;
/**
* 计算除法时，设置的结果标度
*/
int length;
public CalculatorMathUtil(int length) {
this.length = length;
}
/**
* 获得计算结果的字符串表示形式
* @param exp
* @return
*/
public String getResult(String exp) {
this.number = new Stack();
this.operator = new Stack();
calculate(exp);
return this.number.peek().toString();
}
/**
* 对运算式exp进行解析，并计算
* @param exp
*/
public void calculate(String exp) {
int index = 0;
int sign = 0;
while (index < exp.length()) {
char op = exp.charAt(index);
if ((op <= '9' && op >= '0') || op == '.') {
index++;
} else {
if (index > 0) {
char opp = exp.charAt(index-1);
if (op == '-' && !((opp <= '9' && opp >= '0') || opp == '.')) {
index++;
continue;
}
}
if (sign != index) {
String numStr = exp.substring(sign, index);
BigDecimal num = new BigDecimal(numStr);
number.push(num);
}
analysis(op);
sign = ++index;
}
}
}
/**
* 对得到的数据和符号进行分析处理
* @param op
* @param num
*/
public void analysis(char op) {
if (operator.empty() || comparePriority(op, operator.peek())) {
operator.push(op);
} else {
makeNum(op);
}
}
/**
* 计算
* @param op
* @param num
*/
private void makeNum(char op) {
BigDecimal result = null;
while (!operator.empty() && !comparePriority(op, operator.peek())) {
char op2 = operator.pop();
if (op == ')' && op2 == '(') {
return;
}
BigDecimal num1 = null;
BigDecimal num2 = number.pop();
if (number.empty()) {
num1 = new BigDecimal(0);
} else {
num1 = number.pop();
}
switch (op2) {
case '+':
result = num1.add(num2);
break;
case '-':
result = num1.subtract(num2);
break;
case '*':
result = num1.multiply(num2);
break;
case '/':
result = num1.divide(num2, new MathContext(length));
break;
default:
operator.pop();
break;
}
number.push(result);
}
if (op != ')') {
operator.push(op);
}
}
/**
* 判断优先级：true(c1优先级高于c2)、false(c1优先级低于c2)
* @param c1
* @param c2
* @return
*/
public boolean comparePriority(char c1, char c2) {
if (c1 == '=') {
return false;
} else if (c1 == ')') {
return false;
} else if (c1 == '(') {
return true;
} else if (c2 == '(') {
return true;
} else if ((c1 == '*' || c1 == '/') && (c2 == '-' || c2 == '+')) {
return true;
} else {
return false;
}
}
}
CalculatorMainActivity.java
在输入的同时来保证表达式的合法性
import com.anjoyo.lifelittlehelper.R;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class CalculatorMainActivity extends Activity {
private TextView mShowTextView = null;
private StringBuffer mExpressBuffer = new StringBuffer();
private String mResult = "";
private static CalculatorMathUtil mCalculatorMathUtil = new CalculatorMathUtil(20);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_calculator_main);
mShowTextView = (TextView) findViewById(R.id.tv_calculator_result);
}
public void clickMe(View v) {
if (mResult.length() > 0 && mExpressBuffer.toString().contains("=")) {
mExpressBuffer = new StringBuffer();
}
Button btn = (Button) v;
switch (btn.getId()) {
case R.id.btn_calculator_num_0:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(0);
break;
case R.id.btn_calculator_num_1:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(1);
break;
case R.id.btn_calculator_num_2:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(2);
break;
case R.id.btn_calculator_num_3:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(3);
break;
case R.id.btn_calculator_num_4:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(4);
break;
case R.id.btn_calculator_num_5:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(5);
break;
case R.id.btn_calculator_num_6:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(6);
break;
case R.id.btn_calculator_num_7:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(7);
break;
case R.id.btn_calculator_num_8:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(8);
break;
case R.id.btn_calculator_num_9:
if (mExpressBuffer.length() != 0 && mExpressBuffer.charAt(mExpressBuffer.length() - 1) == ')') {
break;
}
mExpressBuffer.append(9);
break;
case R.id.btn_calculator_num_point:
if (mExpressBuffer.length() != 0) {
char c = mExpressBuffer.charAt(mExpressBuffer.length() - 1);
if (c >= '0' && c <= '9') {
mExpressBuffer.append(".");
}
}
break;
case R.id.btn_calculator_brackets_left:
if (mExpressBuffer.length() == 0) {
mExpressBuffer.append("(");
} else {
char c = mExpressBuffer.charAt(mExpressBuffer.length() - 1);
if (c == '+' || c == '-' || c == '*' || c == '/' || c == '(') {
mExpressBuffer.append("(");
}
}
break;
case R.id.btn_calculator_brackets_right:
if (mExpressBuffer.length() != 0) {
char c = '\0';
int n1 = 0;// '('的个数
int n2 = 0;// ')'的个数
for (int i = 0; i < mExpressBuffer.length(); i++) {
c = mExpressBuffer.charAt(i);
if (c == '(') {
n1++;
} else if (c == ')') {
n2++;
}
}
if (n2 < n1 && (c >= '0' && c <= '9' || c == ')')) {
mExpressBuffer.append(")");
}
}
break;
case R.id.btn_calculator_back_space:
if (mExpressBuffer.length() != 0) {
mExpressBuffer.deleteCharAt(mExpressBuffer.length() - 1);
}
break;
case R.id.btn_calculator_operator_0:
mExpressBuffer = new StringBuffer();
mResult = "";
break;
case R.id.btn_calculator_operator_1:
if (mResult.length() != 0) {
mExpressBuffer.append(mResult);
mResult = "";
}
if (mExpressBuffer.length() == 0) {
mExpressBuffer.append("+");
} else {
char c = mExpressBuffer.charAt(mExpressBuffer.length() - 1);
if (c >= '0' && c <= '9' || c == ')') {
mExpressBuffer.append("+");
}
}
break;
case R.id.btn_calculator_operator_2:
if (mResult.length() != 0) {
mExpressBuffer.append(mResult);
mResult = "";
}
if (mExpressBuffer.length() == 0) {
mExpressBuffer.append("-");
} else {
int len = mExpressBuffer.length();
char c = mExpressBuffer.charAt(len - 1);
if (c >= '0' && c <= '9' || c == '(' || c == ')') {
mExpressBuffer.append("-");
} else if (len >= 2) {
c = mExpressBuffer.charAt(len - 2);
if (c >= '0' && c <= '9' || c == '(' || c == ')') {
mExpressBuffer.append("-");
}
}
}
break;
case R.id.btn_calculator_operator_3:
if (mResult.length() != 0) {
mExpressBuffer.append(mResult);
mResult = "";
}
if (mExpressBuffer.length() != 0) {
char c = mExpressBuffer.charAt(mExpressBuffer.length() - 1);
if (c >= '0' && c <= '9' || c == ')') {
mExpressBuffer.append("*");
}
}
break;
case R.id.btn_calculator_operator_4:
if (mResult.length() != 0) {
mExpressBuffer.append(mResult);
mResult = "";
}
if (mExpressBuffer.length() != 0) {
char c = mExpressBuffer.charAt(mExpressBuffer.length() - 1);
if (c >= '0' && c <= '9' || c == ')') {
mExpressBuffer.append("/");
}
}
break;
case R.id.btn_calculator_operator_5:
if (mExpressBuffer.length() != 0) {
char c = '\0';
int n1 = 0;// '('的个数
int n2 = 0;// ')'的个数
for (int i = 0; i < mExpressBuffer.length(); i++) {
c = mExpressBuffer.charAt(i);
if (c == '(') {
n1++;
} else if (c == ')') {
n2++;
}
}
if (n1 == n2 && (c >= '0' && c <= '9' || c == ')')) {
mExpressBuffer.append("=");
try {
mResult = mCalculatorMathUtil.getResult(mExpressBuffer.toString());
mExpressBuffer.append(mResult);
} catch (Exception e1) {
// mExpressBuffer.append(" IS ERROR");
mExpressBuffer.deleteCharAt(mExpressBuffer.length() - 1);
Toast.makeText(this, "表达式错误", Toast.LENGTH_LONG).show();
}
}
}
break;
default:
break;
}
mShowTextView.setText(mExpressBuffer.toString());
}
}
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