带中断的无法访问的语句

2022-01-19 00:00:00 break switch-statement java

所以我有一个先前的问题，但意识到我发布了错误的违规代码.我已经在下面标记了冒犯性的陈述.

So I had a previous question but realized I posted the wrong offending code. I've marked the offending statements below.

我要做的是使用该 switch 语句为每个运算符设置优先级.

What I am trying to do is set the precedence for each of the operators with that switch statement.

也许有人可以为我指明正确的方向.

Maybe someone could point me in the right direction.

请注意，我正在运行 JAVA 7，因此 String Switch 可以工作.

Just as a note, I AM running JAVA 7 so String Switch will work.

代码

opType.java

opType.java

import java.io.*;

public final class opType {

   public static opType ADD = new opType( "Add" );
   public static opType SUB = new opType( "Sub" );
   public static opType MULT = new opType( "Mult" );
   public static opType DIV = new opType( "Div" );
   public static opType MOD = new opType( "Mod" );
   public static opType LPAR = new opType( "LParen" );
   public static opType RPAR = new opType( "RParen" );

   protected String name;

   private opType( String n )
   {
      name = n;
   }

   public String getName()
   {
      return name;
   }

Operator.java

Operator.java

public class Operator extends Token {

    protected opType val;

    public boolean isOperator() { return true; }
    public boolean isOperand() { return false; }

    protected int getPrec()
    {

        switch(val.getName())
        {
            case "LParen": 
            {
                return 0;
                break; //unreachable
            }

            case "RParen": 
            {
                return 0;
                break; //unreachable
            }

            case "Mult":
            {
                return 1;
                break; //unreachable
            }
            case "Div": 
            {   
                return 1;
                break; //unreachable
            }
            case "Mod": 
            {   
                return 1;
                break; //unreachable
            }
            case "Add": 
            {   
                return 2;
                break; //unreachable
            }
            case "Sub": 
            {   
                return 2;
                break; //unreachable
            }
        }

            return 0;
    }

    public static int compare( Operator a, Operator b )
    {
        if( a.getPrec() == b.getPrec() )
            return 0;
        else if( a.getPrec() < b.getPrec() )
            return -1;
        else
            return 1;
    }

    public opType getVal() { return val; }

    public Operator( opType v ) { val = v; }

}

推荐答案

如果你放了一个return，那么函数会在break执行之前返回，因此break 永远不会到达.

If you put a return, then the function returns before the break is executed and therefore the break will never be reached.

相反，您可以使用设置为所需值的变量，并在切换后返回该变量.或者干脆去掉 break 语句.

Instead you could use a variable that you set to a desired value and after the switch return that. Or just get rid of the break statements.

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