Stack Java : Validasi Tanda Kurung

Source code Progam

appStack

StackKurung;
import java.util.Scanner;
public class appStack {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int pilih;
        do{
            System.out.println("");
            System.out.println("PROGRAM VALIDASI");
            System.out.println("1. Validasi Tanda Kurung");
            System.out.println("2. Keluar");
            System.out.print("Pilih : ");
            pilih = s.nextInt();
            switch(pilih){
                case 1:
                    cStack stack = new cStack();
                    System.out.print("Masukkan persamaan : ");
                    s = new Scanner(System.in);
                    String pers = s.nextLine();
                    
                    boolean valid = false;
                    for(int i = 0; i < pers.length(); i++){
                        char t = pers.charAt(i);
                        cItem td = new cItem(t);
                        
                        if(t=='('||t=='{'||t=='['){
                            stack.push(td);
                        }else if(t==')'||t=='}'||t==']'){
                            if(stack.peek()!=null){
                                cItem tpop = stack.pop();
                                if((tpop.getTanda()=='('&& t ==')'||tpop.getTanda()=='{'&&t=='}'||tpop.getTanda()=='['&& t==']')){
                                    valid = true;
                                }
                             }else{
                                valid = false;
                            }
                        }
                    }
                    if(stack.peek()==null&&valid==true){
                        System.out.println("Persamaan Valid(pasangannya)");
                    }else if(stack.peek()!=null&&valid==true){
                        System.out.println("Persamaan Tidak VALID(tidak ada pasangannya)");
                    }else{
                        System.out.println("Persamaan Tidak VALID(bukan pasangan)");
                    }
                    break;
                case 2:
                    System.out.println("Terima Kasih");
            }
            
        }while(pilih!=2);
    }
}

cStack

package StackKurung;
public class cStack {
    cItem top, bottom, temp;
    
    cStack(){
        top = bottom = null;
    }
    
    public void push(cItem baru){
        if(top == null){
            top = bottom = baru;
        }else{
            top.prev = baru;
            baru.next = top;
            top = baru;
        }
    }
    
    public cItem pop(){
        if(top == null){
            return null;
        }else if(top.next == null){
            temp = top;
            top = bottom = null;
            return temp;
        }else{
            temp = top;
            top = top.next;
            temp.next = temp.prev = null;
            return temp;
        }
    }
    
    public cItem peek(){
        if(top == null){
            return null;
        }else{
            return top;
        }
    }
}

cItem

package StackKurung;
public class cItem {
    private char tanda;
    cItem next, prev;
    
    cItem(char t){
        tanda = t;
    }
    
    public char getTanda(){
        return tanda;
    }
}

Hasil Program