[Pin to top] evaluate Java expressions

JAVA expressions are implemented based on the characteristics of advanced stack and later release, for details, see Code

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Public float evaluation (string textfield) {stringbuilder STR = new stringbuilder (); stack <float> STK = new stack <float> (); // used to store operations or result stack <character> stk2 = new stack <character> (); // used to store the stk2.push operator ('#'); // first a '#' in the operator stack for the first operator to compare the priority of char C; // read the character for (INT I = 0; I <textfield. length (); I ++) {Boolean isbeg = false; // whether it is a negative number or a positive number operator C = textfield. charat (I); If (C> = '0' & C <= '9') | C = '. '){ // STR can be directly combined with digits or decimal points. append (c );} else if (C = '+' | C = '-' | C = '*' | C = '/' | C = '( '| C = ') ') {If (C =' + '| C ='-') & STK. empty () & Str. length () = 0) {Str. append (c); isbeg = true;} else if (Str. length ()! = 0) {try {float F = float. parsefloat (Str. tostring (); STK. push (f) ;}catch (exception e) {flag = false; Return-1 ;}str. delete (0, str. length ();} // If the read operator priority is smaller than the element priority on the top of the operator stack, the result is calculated and saved, for example, if (Judge (stk2.peek ()> = judge (c )&&! Isbeg) {try {float B = float. parsefloat (STK. pop (). tostring (); float a = float. parsefloat (STK. pop (). tostring (); // retrieves the two numbers of the operand stack char C1 = stk2.pop (); // retrieves the operator if (C! = ') {Stk2.push (c); // low-priority operator in the stack} switch (C1) {Case' + ': STK. push (a + B); break; Case '-': STK. push (a-B); break; Case '*': STK. push (A * B); break; Case '/': STK. push (A/B); break; default: break;} catch (exception e) {flag = false; Return-1 ;}if (C = ')') {While (stk2.peek ()! = '#') {Float B = float. parsefloat (STK. pop (). tostring (); try {float a = float. parsefloat (STK. pop (). tostring (); // retrieves the two numbers of the operand stack char C1 = stk2.pop (); // retrieves the operator switch (C1) {Case '+': STK. push (a + B); break; Case '-': STK. push (a-B); break; Case '*': STK. push (A * B); break; Case '/': // If (B = 0) {// division to zero //} else {STK. push (A/B); //} break; default: break;} catch (exception e) {flag = false; Return-1 ;}// stk2.pop (); // Pop up ')' stk2. Pop (); // pop up '#'stk2. Pop (); // pop up' ('} else if (! Isbeg) {stk2.push (c); If (C = '(') {stk2.push ('#') ;}} else {flag = false; Return-1 ;}} // if it end with an operand, the last operand is added to the stack if (Str. length ()> 0) {try {float F = float. parsefloat (Str. tostring (); STK. push (f) ;}catch (exception e) {flag = false; Return-1 ;}str. delete (0, str. length ();} // The last character is "(" If (stk2.peek () = '#') {flag = false; Return-1 ;} while (stk2.peek ()! = '#') {Try {float B = float. parsefloat (STK. pop (). tostring (); float a = float. parsefloat (STK. pop (). tostring (); // retrieves the two numbers of the operand stack char C1 = stk2.pop (); // retrieves the operator switch (C1) {Case '+': STK. push (a + B); break; Case '-': STK. push (a-B); break; Case '*': STK. push (A * B); break; Case '/': // If (B = 0) {// division to zero //} else {STK. push (A/B); //} break; default: break; }} catch (exception e) {flag = false; Return-1 ;}try {return float. parsefloat (STK. pop (). tostring ();} catch (exception e) {flag = false; Return-1 ;}}

Determining operator priority

 
// Judge the priority public static int judge (char c) {int n = 0; Switch (c) {Case '(': n = 3; break; Case '+ ': case '-': n = 1; break; Case '*': Case '/': N = 2; break; Case ')': n = 0; break; default:} return N ;}