Java设计模式 - 解释器模式
我们通常使用解释器模式来评估语言语法或表达。
这种类型的模式是行为模式之一。
例子
interface Expression {
public boolean evaluate(String context);
}
class IsInExpression implements Expression {
private String data;
public IsInExpression(String data) {
this.data = data;
}
@Override
public boolean evaluate(String context) {
if (context.contains(data)) {
return true;
}
return false;
}
}
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 evaluate(String context) {
return expr1.evaluate(context) || expr2.evaluate(context);
}
}
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 evaluate(String context) {
return expr1.evaluate(context) && expr2.evaluate(context);
}
}
public class Main {
public static void main(String[] args) {
Expression select = new IsInExpression("Select");
Expression from = new IsInExpression("From");
Expression isSelectFrom = new AndExpression(select, from);
Expression insert = new IsInExpression("Insert");
Expression update = new IsInExpression("Update");
Expression isInsertOrUpdate = new OrExpression(insert, update);
System.out.println(isSelectFrom.evaluate("Select"));
System.out.println(isInsertOrUpdate.evaluate("Insert"));
System.out.println(isSelectFrom.evaluate("Select From"));
System.out.println(isInsertOrUpdate.evaluate("Update"));
}
}
上面的代码生成以下结果。
false
true
true
true