#107 Interpreter example JavaDoc
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Ilkka Seppala
parent
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@ -1,68 +1,72 @@
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package com.iluwatar.interpreter;
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import java.util.Stack;
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/**
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*
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* Interpreter pattern breaks sentences into expressions (Expression) that can
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* be evaluated and as a whole form the result.
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*
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*/
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public class App {
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/**
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*
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* Expressions can be evaluated using prefix, infix or postfix notations
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* This sample uses postfix, where operator comes after the operands
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*
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*/
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public static void main(String[] args) {
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String tokenString = "4 3 2 - 1 + *";
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Stack<Expression> stack = new Stack<>();
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String[] tokenList = tokenString.split(" ");
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for (String s : tokenList) {
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if (isOperator(s)) {
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Expression rightExpression = stack.pop();
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Expression leftExpression = stack.pop();
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System.out
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.println(String.format(
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"popped from stack left: %d right: %d",
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leftExpression.interpret(),
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rightExpression.interpret()));
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Expression operator = getOperatorInstance(s, leftExpression,
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rightExpression);
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System.out.println(String.format("operator: %s", operator));
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int result = operator.interpret();
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NumberExpression resultExpression = new NumberExpression(result);
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stack.push(resultExpression);
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System.out.println(String.format("push result to stack: %d",
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resultExpression.interpret()));
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} else {
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Expression i = new NumberExpression(s);
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stack.push(i);
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System.out.println(String.format("push to stack: %d",
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i.interpret()));
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}
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}
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System.out
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.println(String.format("result: %d", stack.pop().interpret()));
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}
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public static boolean isOperator(String s) {
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return s.equals("+") || s.equals("-") || s.equals("*");
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}
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public static Expression getOperatorInstance(String s, Expression left,
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Expression right) {
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switch (s) {
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case "+":
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return new PlusExpression(left, right);
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case "-":
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return new MinusExpression(left, right);
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case "*":
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return new MultiplyExpression(left, right);
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}
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return null;
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}
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}
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package com.iluwatar.interpreter;
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import java.util.Stack;
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/**
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*
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* Interpreter pattern breaks sentences into expressions ({@link Expression}) that can
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* be evaluated and as a whole form the result.
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*
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*/
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public class App {
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/**
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*
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* Program entry point.
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* <p>
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* Expressions can be evaluated using prefix, infix or postfix notations
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* This sample uses postfix, where operator comes after the operands
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*
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* @param args command line args
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*
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*/
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public static void main(String[] args) {
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String tokenString = "4 3 2 - 1 + *";
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Stack<Expression> stack = new Stack<>();
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String[] tokenList = tokenString.split(" ");
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for (String s : tokenList) {
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if (isOperator(s)) {
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Expression rightExpression = stack.pop();
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Expression leftExpression = stack.pop();
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System.out
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.println(String.format(
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"popped from stack left: %d right: %d",
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leftExpression.interpret(),
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rightExpression.interpret()));
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Expression operator = getOperatorInstance(s, leftExpression,
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rightExpression);
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System.out.println(String.format("operator: %s", operator));
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int result = operator.interpret();
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NumberExpression resultExpression = new NumberExpression(result);
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stack.push(resultExpression);
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System.out.println(String.format("push result to stack: %d",
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resultExpression.interpret()));
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} else {
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Expression i = new NumberExpression(s);
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stack.push(i);
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System.out.println(String.format("push to stack: %d",
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i.interpret()));
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}
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}
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System.out
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.println(String.format("result: %d", stack.pop().interpret()));
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}
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public static boolean isOperator(String s) {
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return s.equals("+") || s.equals("-") || s.equals("*");
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}
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public static Expression getOperatorInstance(String s, Expression left,
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Expression right) {
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switch (s) {
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case "+":
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return new PlusExpression(left, right);
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case "-":
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return new MinusExpression(left, right);
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case "*":
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return new MultiplyExpression(left, right);
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}
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return null;
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}
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}
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@ -1,9 +1,14 @@
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package com.iluwatar.interpreter;
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public abstract class Expression {
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public abstract int interpret();
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@Override
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public abstract String toString();
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}
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package com.iluwatar.interpreter;
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/**
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*
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* Expression
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*
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*/
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public abstract class Expression {
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public abstract int interpret();
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@Override
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public abstract String toString();
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}
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@ -1,23 +1,28 @@
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package com.iluwatar.interpreter;
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public class MinusExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public MinusExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() - rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "-";
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}
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}
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package com.iluwatar.interpreter;
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/**
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*
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* MinusExpression
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*
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*/
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public class MinusExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public MinusExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() - rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "-";
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}
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}
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@ -1,24 +1,29 @@
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package com.iluwatar.interpreter;
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public class MultiplyExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public MultiplyExpression(Expression leftExpression,
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Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() * rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "*";
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}
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}
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package com.iluwatar.interpreter;
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/**
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*
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* MultiplyExpression
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*
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*/
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public class MultiplyExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public MultiplyExpression(Expression leftExpression,
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Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() * rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "*";
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}
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}
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@ -1,25 +1,30 @@
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package com.iluwatar.interpreter;
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public class NumberExpression extends Expression {
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private int number;
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public NumberExpression(int number) {
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this.number = number;
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}
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public NumberExpression(String s) {
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this.number = Integer.parseInt(s);
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}
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@Override
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public int interpret() {
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return number;
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}
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@Override
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public String toString() {
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return "number";
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}
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}
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package com.iluwatar.interpreter;
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/**
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*
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* NumberExpression
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*
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*/
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public class NumberExpression extends Expression {
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private int number;
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public NumberExpression(int number) {
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this.number = number;
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}
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public NumberExpression(String s) {
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this.number = Integer.parseInt(s);
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}
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@Override
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public int interpret() {
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return number;
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}
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@Override
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public String toString() {
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return "number";
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}
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}
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@ -1,23 +1,28 @@
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package com.iluwatar.interpreter;
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public class PlusExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public PlusExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() + rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "+";
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}
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}
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package com.iluwatar.interpreter;
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/**
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*
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* PlusExpression
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*
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*/
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public class PlusExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public PlusExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() + rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "+";
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}
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}
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@ -1,14 +1,19 @@
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package com.iluwatar.interpreter;
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import org.junit.Test;
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import com.iluwatar.interpreter.App;
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public class AppTest {
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@Test
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public void test() {
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String[] args = {};
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App.main(args);
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}
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}
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package com.iluwatar.interpreter;
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import org.junit.Test;
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import com.iluwatar.interpreter.App;
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/**
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*
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* Application test
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*
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*/
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public class AppTest {
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@Test
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public void test() {
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String[] args = {};
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App.main(args);
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}
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}
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