代码来自闵老师”日撸 Java 三百行(21-30天)“,链接:https://blog.csdn.net/minfanphd/article/details/116975721
package datastructure.stack;
/**
*
* Object stack.
*
* @author WX873
*
*/
public class ObjectStack {
/**
* The depth.
*/
public static final int MAX_DEPTH = 10;
/**
* The data.
*/
Object[] data;
/**
* The actual depth.
*/
int depth;
/**
* construct an empty char stack.
*/
public ObjectStack() {
// TODO Auto-generated constructor stub
depth = 0;
data = new Object[MAX_DEPTH];
}//of the first constructor
/**
* ***********************************************************
* Overrides the method claimed in Object, the superclass of any class.
* ***********************************************************
*/
public String toString() {
String resultString = "";
if (depth == 0) {
System.out.println("The stack is empty!");
return null;
}//of if
for (int i = 0; i < depth; i++) {
resultString += data[i] + ", ";
}//of for i
return resultString;
}//of toString
/**
* **************************************************************
* Push an element.
*
* @param paraObject The given Object.
* @return Push success or not.
* **************************************************************
*/
public boolean push(Object paraObject) {
if (depth == MAX_DEPTH) {
System.out.println("Stack full.");
return false;
}//of if
data[depth] = paraObject;
depth++;
return true;
}//of push
/**
* *************************************************************
* Pop an element.
*
* @return The Object at the top of the stack.
* *************************************************************
*/
public Object pop() {
if (depth == 0) {
System.out.println("No element to pop!");
return '\0';
}//of if
depth--;
return data[depth];
}//of pop
/**
* ************************************************************
* Is the stack empty?
*
* @return True, if empty.
* ************************************************************
*/
public boolean isEmpty() {
if (depth == 0) {
System.out.println("The stack is empty!");
return true;
}//of if
return false;
}//of isEmpty
/**
* ************************************************************
* The entrance of the program.
*
* @param args Not used now.
* ************************************************************
*/
public static void main(String args[]) {
ObjectStack tempStack = new ObjectStack();
for (char ch = 'a'; ch < 'm'; ch++) {
tempStack.push(new Character(ch));
System.out.println("The current stack is: " + tempStack.toString());
}//of for ch
char tempChar;
for (int i = 0; i < 12; i++) {
tempChar = ((Character)tempStack.pop()).charValue();
System.out.println("Poped: " + tempChar);
System.out.println("The current stack is: " + tempStack.toString());
}//of for i
}//of main
}//of ObjectStack
这里自己写代码的时候,将pop()中的if语句里的返回值写成了“return null;”,结果运行的时候就报错。网上查了一下,‘\0’表示空字符。相当于这里还是有返回值,只是返回值为空字符。
return null;方法的返回值必须不是原始数据类型(封装类除外)和void。return 就是跳出方法;return null也是跳出方法并返回null。不要认为null就是没有值,null就是值。
原始类型 | 封装类
boolean | Boolean
char | Character
byte | Byte
short | Short
int | Integer
long | Long
float | Float
double | Double
关于原始类型与原始封装类的介绍:https://www.cnblogs.com/wisdo/p/4915774.html
/**
* ******************************************************
* In-order visit with stack.
* ******************************************************
*/
public void inOrderVisitWithStack() {
ObjectStack tempStack = new ObjectStack();
BinaryCharTree tempNode = this;
while (!tempStack.isEmpty() || tempNode != null) {
if (tempNode != null) {
tempStack.push(tempNode);
tempNode = tempNode.leftChild;
} else {
tempNode = (BinaryCharTree) tempStack.pop();
System.out.println("" + tempNode.value + "");
tempNode = tempNode.rightChild;
}
}//of while
}//of inOrderVisitWithStack
/**
* *********************************************************
* The entrance of the program.
*
* @param args Not used now
* *********************************************************
*/
public static void main(String args[]) {
BinaryCharTree tempTree = manualConstructTree();
System.out.println("\r\nPre-order visit:");
tempTree.preOrderVisit();
System.out.println("\r\nIn-order visit:");
tempTree.inOrderVisit();
System.out.println("\r\nPost-order visit:");
tempTree.postOrderVisit();
int tempDepth = tempTree.getDepth();
System.out.println("\nThe depth is: " + tempDepth);
System.out.println("\rThe number of nodes for the binary tree is: " + tempTree.getNumNodes());
tempTree.toDataArrays();
System.out.println("The values are: " + Arrays.toString(tempTree.valueArray));
System.out.println("The indices are: " + Arrays.toString(tempTree.indicesArray));
tempTree.toDataArraysObjectQueue();
System.out.println("Only object queue.");
System.out.println("The values are: " + Arrays.toString(tempTree.valueArray));
System.out.println("The indices are: " + Arrays.toString(tempTree.indicesArray));
tempTree.toDataArrayGenericQueue();
System.out.println("Generic queue.");
System.out.println("The values are: " + Arrays.toString(tempTree.valueArray));
System.out.println("The indices are: " + Arrays.toString(tempTree.indicesArray));
//char[] tempCharArray = {'A','B','C','D','E','F'};
//int[] tempIndicesArray = {0, 1, 2, 4, 5, 12};
char[] tempCharArray = {'a','b','c','d','e','f','g'};
int[] tempIndicesArray = {0, 1, 2, 4, 5, 9, 10};
BinaryCharTree tempTree2 = new BinaryCharTree(tempCharArray, tempIndicesArray);
System.out.println("\r\nPre-order visit:");
tempTree2.preOrderVisit();
System.out.println("\r\nIn-order visit:");
tempTree2.inOrderVisit();
System.out.println("\r\nPost-order visit:");
tempTree2.postOrderVisit();
System.out.println("\r\nIn-order visit with stack:");
tempTree2.inOrderVisitWithStack();
}//of main
inOrderVisitWithStack()的设计思路相当巧妙,用一个while循环同时实现了入栈和出栈;入栈后指向左孩子节点,出栈后指向右孩子节点。