achieve
We will create an interface Expression and an entity class that implements the Expression interface.
The TerminalExpression class that defines terminal expressions . The non-terminal expression classes OrExpression and AndExpression are used to create combined expressions.
InterpreterPatternDemo , our presentation class uses the Expression class to create rules and demonstrate expression parsing.
The first step is to create an expression interface
/**
* 表达式接口
*/
public interface Expression {
public boolean interpret(String context);
}
The second step is to create a terminal expression
/**
* 终端表达式
*/
public class TerminalExpression implements Expression {
private String data;
public TerminalExpression(String data){
this.data = data;
}
@Override
public boolean interpret(String context) {
if(context.contains(data)){
return true;
}
return false;
}
}
The third step is to create a non-terminal expression
/**
* 非终端表达式、或运算
*/
public class OrExpression implements Expression {
private Expression expr1 = null;
private Expression expr2 = null;
public OrExpression(Expression expr1, Expression expr2) {
this.expr1 = expr1;
this.expr2 = expr2;
}
@Override
public boolean interpret(String context) {
return expr1.interpret(context) || expr2.interpret(context);
}
}
/**
* 非终端表达式、与运算
*/
public class AndExpression implements Expression {
private Expression expr1 = null;
private Expression expr2 = null;
public AndExpression(Expression expr1, Expression expr2) {
this.expr1 = expr1;
this.expr2 = expr2;
}
@Override
public boolean interpret(String context) {
return expr1.interpret(context) && expr2.interpret(context);
}
}
The fourth step, the test
package interpreter.demo1;
/**
* 测试类
*/
public class Client {
//规则:Robert 和 John 是男性
public static Expression getMaleExpression(){
Expression robert = new TerminalExpression("Robert");
Expression john = new TerminalExpression("John");
return new OrExpression(robert, john);
}
//规则:Julie 是一个已婚的女性
public static Expression getMarriedWomanExpression(){
Expression julie = new TerminalExpression("Julie");
Expression married = new TerminalExpression("Married");
return new AndExpression(julie, married);
}
public static void main(String[] args) {
Expression isMale = getMaleExpression();
Expression isMarriedWoman = getMarriedWomanExpression();
System.out.println("John is male? " + isMale.interpret("John"));
System.out.println("Julie is a married women? "+ isMarriedWoman.interpret("Married Julie"));
}
}
John is male? true
Julie is a married women? true