解释器模式

src/main/java/top/fjy8018/designpattern/pattern/behavior/interpreter/AddInterpreter.java

@@ -0,0 +1,31 @@
+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+/**
+ * 加法解释器
+ *
+ * @author F嘉阳
+ * @date 2020/3/5 14:46
+ */
+public class AddInterpreter implements Interpreter {
+
+    /**
+     * 定义两个表达式
+     */
+    private Interpreter firstExpression, secondExpression;
+
+    public AddInterpreter(Interpreter firstExpression, Interpreter secondExpression) {
+        this.firstExpression = firstExpression;
+        this.secondExpression = secondExpression;
+    }
+
+    @Override
+    public int interpret() {
+        // 此时传入为NumberInterpreter类型，调interpret方法转int类型
+        return this.firstExpression.interpret() + this.secondExpression.interpret();
+    }
+
+    @Override
+    public String toString() {
+        return "+";
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/interpreter/CustomExpressionParser.java

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+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+import lombok.extern.slf4j.Slf4j;
+
+import java.util.Stack;
+
+/**
+ * @author F嘉阳
+ * @date 2020/3/5 14:48
+ */
+@Slf4j
+public class CustomExpressionParser {
+    private Stack<Interpreter> stack = new Stack<Interpreter>();
+
+    public int parse(String str) {
+        String[] strItemArray = str.split(" ");
+        for (String symbol : strItemArray) {
+            if (!OperatorUtil.isOperator(symbol)) {
+                Interpreter numberExpression = new NumberInterpreter(symbol);
+                stack.push(numberExpression);
+                log.info(String.format("入栈: %d", numberExpression.interpret()));
+            } else {
+                //是运算符号，可以计算
+                Interpreter firstExpression = stack.pop();
+                Interpreter secondExpression = stack.pop();
+                log.info(String.format("出栈: %d 和 %d",
+                        firstExpression.interpret(), secondExpression.interpret()));
+                Interpreter operator = OperatorUtil.getExpressionObject(firstExpression, secondExpression, symbol);
+                log.info(String.format("应用运算符: %s", operator));
+                int result = operator.interpret();
+                NumberInterpreter resultExpression = new NumberInterpreter(result);
+                stack.push(resultExpression);
+                log.info(String.format("阶段结果入栈: %d", resultExpression.interpret()));
+            }
+        }
+        int result = stack.pop().interpret();
+        return result;
+
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/interpreter/Interpreter.java

@@ -0,0 +1,15 @@
+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+/**
+ * 解释器
+ * <p>
+ * JDK 源码
+ * {@link java.util.regex.Pattern} 正则解释器
+ * {@link org.springframework.expression.spel.standard.SpelExpressionParser} Spring解释器
+ *
+ * @author F嘉阳
+ * @date 2020/3/5 14:45
+ */
+public interface Interpreter {
+    int interpret();
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/interpreter/MultiInterpreter.java

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+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+/**
+ * 乘法解释器
+ *
+ * @author F嘉阳
+ * @date 2020/3/5 14:47
+ */
+public class MultiInterpreter implements Interpreter {
+
+    private Interpreter firstExpression, secondExpression;
+
+    public MultiInterpreter(Interpreter firstExpression, Interpreter secondExpression) {
+        this.firstExpression = firstExpression;
+        this.secondExpression = secondExpression;
+    }
+
+    @Override
+    public int interpret() {
+        return this.firstExpression.interpret() * this.secondExpression.interpret();
+    }
+
+    @Override
+    public String toString() {
+        return "*";
+    }
+
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/interpreter/NumberInterpreter.java

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+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+/**
+ * @author F嘉阳
+ * @date 2020/3/5 14:47
+ */
+public class NumberInterpreter implements Interpreter {
+    private int number;
+
+    public NumberInterpreter(int number) {
+        this.number = number;
+    }
+
+    public NumberInterpreter(String number) {
+        this.number = Integer.parseInt(number);
+    }
+
+    @Override
+    public int interpret() {
+        return this.number;
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/behavior/interpreter/OperatorUtil.java

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+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+/**
+ * @author F嘉阳
+ * @date 2020/3/5 14:47
+ */
+public class OperatorUtil {
+    public static boolean isOperator(String symbol) {
+        return (symbol.equals("+") || symbol.equals("*"));
+
+    }
+
+    public static Interpreter getExpressionObject(Interpreter firstExpression, Interpreter secondExpression, String symbol) {
+        if (symbol.equals("+")) {
+            return new AddInterpreter(firstExpression, secondExpression);
+        } else if (symbol.equals("*")) {
+            return new MultiInterpreter(firstExpression, secondExpression);
+        }
+        return null;
+    }
+}

src/test/java/top/fjy8018/designpattern/pattern/behavior/interpreter/InterpreterTest.java

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+package top.fjy8018.designpattern.pattern.behavior.interpreter;
+
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Test;
+import org.springframework.expression.Expression;
+import org.springframework.expression.spel.standard.SpelExpressionParser;
+
+/**
+ * @author F嘉阳
+ * @date 2020/3/5 14:48
+ */
+@Slf4j
+class InterpreterTest {
+
+    @Test
+    void interpret() {
+        String myInterpreter = "6 100 11 + *";
+        CustomExpressionParser expressionParser = new CustomExpressionParser();
+        int result = expressionParser.parse(myInterpreter);
+        log.info("解释器计算结果: " + result);
+    }
+
+    @Test
+    void springTest() {
+        org.springframework.expression.ExpressionParser parser = new SpelExpressionParser();
+        Expression expression = parser.parseExpression("100 * 2 + 400 * 1 + 66");
+        int result = (Integer) expression.getValue();
+        log.info(String.valueOf(result));
+    }
+}