Java Tutorial/Collections/Your Stack
Содержание
A stack allows access to only one data item: the last item inserted
- Push: To insert a data item on the stack
- Pop : To remove a data item from the top of the stack
- Peek: Read the value from the top of the stack without removing it.
<source lang="java">
class Stack {
private int maxSize;
private double[] stackArray;
private int top;
public Stack(int s) {
maxSize = s;
stackArray = new double[maxSize];
top = -1;
}
public void push(double j) {
stackArray[++top] = j;
}
public double pop() {
return stackArray[top--];
}
public double peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
public boolean isFull() {
return (top == maxSize - 1);
}
} public class MainClass {
public static void main(String[] args) {
Stack theStack = new Stack(10);
theStack.push(20);
theStack.push(40);
theStack.push(60);
theStack.push(80);
while (!theStack.isEmpty()) {
double value = theStack.pop();
System.out.print(value);
System.out.print(" ");
}
System.out.println("");
}
}</source>
80.0 60.0 40.0 20.0
Demonstrating a stack implemented as a list
<source lang="java">
class Link {
public int iData;
public Link next;
public Link(int id) {
iData = id;
}
public String toString() {
return "{" + iData + "} ";
}
} class LinkList {
private Link first;
public LinkList() {
first = null;
}
public boolean isEmpty() {
return (first == null);
}
public void insertFirst(int dd) {
Link newLink = new Link(dd);
newLink.next = first;
first = newLink;
}
public int deleteFirst() {
Link temp = first;
first = first.next;
return temp.iData;
}
public String toString() {
String str="";
Link current = first;
while (current != null) {
str += current.toString();
current = current.next;
}
return str;
}
} class LinkStack {
private LinkList theList;
public LinkStack() {
theList = new LinkList();
}
public void push(int j) {
theList.insertFirst(j);
}
public double pop() {
return theList.deleteFirst();
}
public boolean isEmpty() {
return (theList.isEmpty());
}
public String toString() {
return theList.toString();
}
} public class MainClass {
public static void main(String[] args) {
LinkStack theStack = new LinkStack();
theStack.push(20);
theStack.push(40);
System.out.println(theStack);
theStack.push(60);
theStack.push(80);
System.out.println(theStack);
theStack.pop();
theStack.pop();
System.out.println(theStack);
}
}</source>
{40} {20}
{80} {60} {40} {20}
{40} {20}
Stack Example: Delimiter Matching
This time we use the Stack class from Java library.
Using stack to check matching brackets
Examples:
- c[d] // correct
- a{b[c]d}e // correct
- a{b(c]d}e // not correct; ] doesn"t match (
- a[b{c}d]e} // not correct; nothing matches final }
- a{b(c) // not correct; Nothing matches opening {
<source lang="java">
import java.util.Stack; class BracketChecker {
private String input;
public BracketChecker(String in) {
input = in;
}
public void check() {
Stack<Character> theStack = new Stack<Character>();
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
switch (ch) {
case "{":
case "[":
case "(":
theStack.push(ch);
break;
case "}":
case "]":
case ")":
if (!theStack.isEmpty()) {
char chx = theStack.pop();
if ((ch == "}" && chx != "{") || (ch == "]" && chx != "[") || (ch == ")" && chx != "("))
System.out.println("Error: " + ch + " at " + j);
} else
System.out.println("Error: " + ch + " at " + j);
break;
default:
break;
}
}
if (!theStack.isEmpty()){
System.out.println("Error: missing right delimiter");
}
}
} public class MainClass {
public static void main(String[] args) {
String input;
input = "[]]()()";
BracketChecker theChecker = new BracketChecker(input);
theChecker.check();
}
}</source>
Error: ] at 2
Using stack to reverse a string
<source lang="java">
class Stack {
private int maxSize;
private char[] stackArray;
private int top;
public Stack(int s) {
maxSize = s;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
public boolean isFull() {
return (top == maxSize - 1);
}
} public class MainClass {
public static void main(String[] args) {
String input = "input";
int stackSize = input.length();
Stack theStack = new Stack(stackSize);
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
theStack.push(ch);
}
while (!theStack.isEmpty()) {
char ch = theStack.pop();
System.out.println(ch);
}
}
}</source>
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