Java表达式求值、杨辉三角实验报告

一．实验目的

实现杨辉三角和表达式的封装

二．实验软件环境

本实验是在MyEclipse 9.01M1编写和运行的

三．实验内容

（一）实验要求

1. 输出杨辉三角前N项，N为参数

2. 表达式求值：输入一个表达式，输出它的值，其中要用到java.util.Stack （二）实验代码

程序代码：

1）杨辉三角：

/**

*功能：用二维数组实现杨辉三角

*时间：2011-05-01

**/

package https://www.360docs.net/doc/758690075.html,b1;

import java.io.*;

public class Pascal{

public Pascal(){

play();

}

public void play(){

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

System.out.print("请输入n值:");

int n = 0;

try {

n = Integer.parseInt(br.readLine());

} catch (NumberFormatException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

int array[][] = new int[n][2*n-1];

//判断是否为奇数

if( n%2 == 1 ){

for(int i=1; i<=n; i++){

for(int j=1; j<=2*n-1 ;j++){

//首先给前5-i个元素赋值0

if(j<=n-i)

array[i-1][j-1] = 0;

//输出第一个“1”和最后一个“1”

else if((j==(n-i+1))||(j==n+i-1))

array[i-1][j-1] = 1;

else if((j < n+i-1)&&(j > n-i+1)){

if((j-i)%2 == 1)

array[i-1][j-1] = 0;

else

array[i-1][j-1] = array[i-2][j-2] + array[i-2][j];

}

}

}

}

//为偶数所进行的操作

else{

for(int i=1; i<=n; i++){

for(int j=1; j<=2*n-1; j++){

//首先给前5-i个元素赋值0

if(j<=n-i)

array[i-1][j-1] = 0;

//输出第一个“1”和最后一个“1”

else if((j==(n-i+1))||(j==n+i-1))

array[i-1][j-1] = 1;

else if((j < n+i-1)&&(j > n-i+1)){

if((j-i)%2 == 0)

array[i-1][j-1] = 0;

else

array[i-1][j-1] = array[i-2][j-2] + array[i-2][j];

}

}

}

}

/*输出数组*/

for(int i=1; i<=n; i++){

for(int j=1; j<=2*n-1; j++){

if(array[i-1][j-1] == 0){

System.out.print(" ");

}

else

System.out.print(array[i-1][j-1]);

System.out.print(" ");

}

System.out.println();

}

}

public static void main(String argc[]){

Pascal p = new Pascal();

}

}

2）表达式求值，代码如下：

1）Stack类：用来存储表达式子元素的类，代码如下：

package https://www.360docs.net/doc/758690075.html,btwo;

public class Stack {

private int maxLen;

private int size;

private char c[];

public Stack(int maxLen) {

this.maxLen = maxLen;

c = new char[maxLen];

size = 0;

}

public void push(char v){

c[size++] = v;

}

public char pop(){

return c[--size];

}

public boolean isEmpty(){

return size == 0;

}

}

2）ExplainPostfix类：实现将输入的表达式转成后缀表达式，代码如下：

package https://www.360docs.net/doc/758690075.html,btwo; public class ExplainPostfix {

String in; String out = "";

Stack s;

public ExplainPostfix(String in){

System.out.println("计算表达式

为:"+in);

this.in = in;

}

public void display(){

System.out.println("后缀表达式

为:"+out);

}

//转换成后缀表达式

public void toPraser(){

s = new Stack(in.length());

for(int i=0;i

char c = in.charAt(i);

switch(c){

case'+':

case'-':

getOpter(c,1);

break;

case'*':

case'/':

getOpter(c,2);

break;

case'(':

s.push(c);

break;

case')':

getParen();

break;

default:

out = out + c;

}

}

while(!s.isEmpty()){

out = out + s.pop();

}

}

public void getOpter(char c,int prec1){ out = out + 'a';

while(!s.isEmpty()){

char optop = s.pop();

if(optop == '('){

s.push(optop);

break;

}

else{

int prec2 = 0;

if(optop == '+' || optop

== '-'){

prec2 = 1;

}

else{

prec2 = 2;

}

if(prec1>prec2){

s.push(optop);

break;

}

else{

System.out.println("o

p:"+optop);

out = out + optop;

}

}

}

s.push(c);

}

public void getParen(){

while(!s.isEmpty()){

char c = s.pop();

if(c == '(')

break;

else

out = out + c;

}

}

public static void main(String[] args) {

ExplainPostfix p = new

ExplainPostfix("(11+2)*5");

p.toPraser();

p.display();

}

}

3）CalculateExpression类：功能实现将后缀表达式进行计算，代码如下：

package https://www.360docs.net/doc/758690075.html,btwo;

public class CalculateExpression {

String in;

Stack s; public CalculateExpression(String in) { this.in = in;

}

public CalculateExpression(){

play();

}

public static void main(String args[]){

ExplainPostfix p1 = new

ExplainPostfix("(21+4)*(1+3*2)");

p1.toPraser();

p1.display();

CalculateExpression p = new

CalculateExpression(p1.out);

p.doPraser();

p.display();

}

//开始计算后缀表达式

public void doPraser(){

while(true){

int a,b,c,d;

a = in.indexOf("+");

b = in.indexOf("-");

c = in.indexOf("*");

d = in.indexOf("/");

int n = Math.max(a, b);

n = Math.max(n, c);

n = Math.max(n, d);

if(a != -1){

n = a;

}

if(b

n = b;

}

if(c

n = c;

}

if(d

n =d;

}

if(a == -1 && b == -1 && c == -1 && d == -1){

break;

}

String s1 = charAt(n-1);

String s2 =

charAt(n-2-s1.length());

int v = 0;

if(n == a){

v = Integer.parseInt(s1) +

Integer.parseInt(s2);

}

else if(n == b){

v = Integer.parseInt(s2) -

Integer.parseInt(s1);

}

else if(n == c){

v = Integer.parseInt(s2) *

Integer.parseInt(s1);

}

else{

v = Integer.parseInt(s2) /

Integer.parseInt(s1);

}

String s = ""+v;

if(s.equals("0")){

s = "";

}

else{

s = s +"a";

}

in =

in.substring(0,https://www.360docs.net/doc/758690075.html,stIndexOf(s2))

+v+

in.substring(n+1,in.length());

}

}

public void display(){

System.out.println("结果为:"+in);

}

public String charAt(int i){

String str = "";

char c = in.charAt(i);

if(c == '+' || c == '-' || c == '*' || c == '/'){

str = str + c;

return str;

}

else{

while(c != 'a'){

str = c + str ;

if(i == 0){

break;

}

c = in.charAt(--i);

if(c == '+' || c == '-' || c == '*' || c == '/'){

break;

}

}

}

return str;

}

}

四．实验的结果及分析

1. 杨辉三角结果：

2. 算术表达式结果：

五．实验心得体会

试验后熟悉封装思想，使用基本Java算法。