Java 堆栈与 ArrayList
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Java Stacks With ArrayList
提问by SomeSickJoke
Hey guys ive come stuck once again, I can manage to push items onto a stack and pop them off. I even got working a stack with open and close brackets. But when I come to do it with ()or {}or []brackets with my code I created it seems to ignore the if statement and goes to else any ideas why.
嘿伙计们，我再次卡住了，我可以设法将项目推入堆栈并将其弹出。我什至开始使用带有开括号和闭括号的堆栈。但是，当我带着做()或{}或[]我的代码括号我创造它似乎忽略if语句，去到别的任何想法，为什么。
Main.java
主程序
public class DifferentBrackets {
public static void main(String[] args) {
Stack brackets = new Stack();
Scanner k = new Scanner(System.in);
System.out.println("* to Terminate or Enter bracket : ");
String tempBrack = k.next();
while (!tempBrack.equals("*")) {
System.out.println("* to Terminate or Enter bracket : ");
switch (tempBrack) {
case "(":
brackets.push("(");
System.out.println(tempBrack + " is added");
break;
case "{":
brackets.push("{");
System.out.println(tempBrack + " is added");
break;
case "[":
brackets.push("[");
System.out.println(tempBrack + " is added");
break;
case ")":
if (tempBrack.equals(brackets.arrayTop()))
{
System.out.println(brackets.pop() + " is popped");
}
else if(tempBrack.equals(brackets.arrayTop()))
{
System.out.println("Closed Bracket Doesnt Match Top Open Bracket");
}
else
{
System.out.println("Closed Bracket Doesnt Match Top Open Bracket");
}
break;
// case "}":
// if (tempBrack.equals(brackets.arrayTop()))
// {
// System.out.println(brackets.pop() + " is popped");
// }
// else if (!tempBrack.equals(brackets.arrayTop()))
// {
// System.out.println("Closed Bracket Doesnt Match Top Open Bracket");
// }
//
// break;
// case "]":
// if (tempBrack.equals(brackets.arrayTop()))
// {
// if (!tempBrack.equals(brackets.arrayTop()))
// {
// System.out.println("Closed Bracket Doesnt Match Top Open Bracket");
// }
// break;
}
System.out.println("* to Terminate or Enter bracket : ");
tempBrack = k.next();
}
}
}
Heres my Stack.java
这是我的 Stack.java
import java.util.ArrayList;
public class Stack
{
private ArrayList<String> a;
public Stack()
{
a = new ArrayList(10); //initial capacity of 10
}
public boolean isEmpty()
{
return a.isEmpty();
}
public String pop() //pop integer element
{
String last;
last = a.remove((a.size()- 1));
return(last); //underflow will crash
}
public void push(String x) //push integer element
{
a.add(x);
}
public String arrayTop()
{
return(a.get(a.size() -1));
}
}
采纳答案by Alexis C.
When you add a ")"you want to check if the top of the stack contains a "(", not a ")". But this is what you actually test here.
当您添加 a 时，")"您想检查堆栈顶部是否包含 a "("，而不是 a ")"。但这就是您在这里实际测试的内容。
if (tempBrack.equals(brackets.arrayTop()))
is the same as (let's say your stack contains just "("and you entered ")") :
与（假设您的堆栈只包含"("您输入的")"）相同：
if (")".equals("("))
which is obviously false.
这显然是错误的。
You have to make the check in a way that when you're in a closing parenthesis/bracket, you have to check if the top of the stack contains an openingone.
你必须做的方式，当你在一个右括号/支架的时候，你必须检查堆栈的顶部包含一个检查口之一。
case ")":
if ("(".equals(brackets.arrayTop())){
System.out.println(brackets.pop() + " is popped");
}
else {
System.out.println("Closed Bracket Doesnt Match Top Open Bracket");
}
break;
The same logic applies for "{"and "[".
同样的逻辑适用于"{"和"["。
Note that :
注意 ：
- The API already provides a Stackclass, no need to reinvent the wheel, you should use this one.
- Consider using a Stack of
Characters, notStrings - You may end your program if a closing bracket doesn't match a top open one.
- API 已经提供了一个Stack类，不需要重新发明轮子，你应该使用这个。
- 考虑使用 Stack of
Characters，而不是Strings - 如果右括号与顶部开括号不匹配，您可以结束程序。
回答by robbmj
Please see the comments for an explanation. To the OP, please read and understand ZouZou's answer.
请参阅评论以获取解释。对于OP，请阅读并理解邹走的回答。
import java.util.Scanner;
public class DifferentBrackets {
public static void main(String[] args) {
Stack brackets = new Stack();
Scanner k = new Scanner(System.in);
System.out.println("* to Terminate or Enter bracket : ");
String tempBrack = k.next();
while (!tempBrack.equals("*")) {
// if the user added an opening bracket
// push it on the stack
if (isOpeningBracket(tempBrack)) {
brackets.push(tempBrack);
}
else if (isClosingBracket(tempBrack)) {
// first check to see of the element at the
// top of the stack is the mirror of the closing bracket
if (brackets.arrayTop().equals(mirror(tempBrack))) {
// if it is pop it from the stack
System.out.println(brackets.pop() + " is popped");
}
else {
System.out.println("Closed Bracket Doesnt Match Top Open Bracket");
}
}
else {
System.out.println(tempBrack + " is an unsuported character");
}
tempBrack = k.next();
}
// if there is nothing on the stack after the user enters "*"
// the user has entered balanced brackets
if (brackets.isEmpty()) {
System.out.println("Congrats your brackets are balanced");
}
else {
System.out.println("Sorry your brackets are not balanced");
}
k.close();
}
// find the closing bracket's mirror
public static String mirror(String str) {
switch (str) {
case ")":
return "(";
case "]":
return "[";
case "}":
return "{";
default:
return null;
}
}
public static boolean isOpeningBracket(String str) {
return str.equals("(") || str.equals("{") || str.equals("[");
}
public static boolean isClosingBracket(String str) {
return str.equals(")") || str.equals("}") || str.equals("]");
}
}
