链表对象的substring()方法 [英] substring() method for linked list object
问题描述
我在为正在构建的名为 LString
的类编写 substring()
方法时遇到了一些麻烦.此类创建一个名为 LString
的链接列表对象,该对象将构建字符串.它模仿Java中的 String
和 StringBuilder
对象.
I'm having some trouble writing a substring()
method for a class I'm building called LString
. This class creates a linked list object called LString
that builds strings. It mimics the String
and StringBuilder
objects in Java.
substring(int start,int end)
根据给定的 this
LString从提供的索引中创建一个新的
至 LString
>开始结束
.它返回类型 LString
.
substring(int start, int end)
creates a new LString
out of the given this
LString, from the index provided by start
to end
. It returns type LString
.
以下是错误消息,未进行任何编辑以使 end
包括在内:
Here is the error message without any edits to make end
inclusive:
Running substring tests (63 tests)
Starting tests: ......E........................................................
Time: 0.031
There was 1 failure:
1) test43cSubStringOneChar(LStringTest$LStringSubStringTestSpecial)
java.lang.AssertionError: Substring of One Character LString is not equals LString expected: LString<a> but was: LString<a>
at org.junit.Assert.fail(Assert.java:88)
at org.junit.Assert.failNotEquals(Assert.java:743)
at org.junit.Assert.assertEquals(Assert.java:118)
at LStringTest$LStringSubStringTestSpecial.test43cSubStringOneChar(LStringTest.java:401)
... 10 more
Test Failed! (1 of 63 tests failed.)
Test failures: abandoning other phases.
这会产生一条更简单的错误消息,只有1个失败.
This produces a simpler error message, with only 1 failure.
以下是与该错误消息相对应的代码:
Here is the code corresponding to that error message:
import java.io.*;
import java.util.*;
public class LString {
node front;
int size;
//Creating a node class
private class node {
char data;
node next;
public node (){
}
public node (char newData){
this.data = newData;
}
public node (char newData, node newNext){
this.data = newData;
this.next = newNext;
}
}
//Constructors
public LString(){
this.size = 0;
this.front = null;
}
public LString(String original) {
this.size = original.length();
if (original.length() > 0){
this.front = new node(original.charAt(0));
node curr = this.front;
for (int i =1; i < original.length(); i++) {
curr.next = new node(original.charAt(i));
curr = curr.next;
}
}
}
// Length method, returns the length of LString
public int length() {
return this.size;
}
// compareTo method, compares this LString to anotherLString, returns 0 if equal,
// -1 if lexicogrpahically less, and 1 if lexicographically greater
public int compareTo(LString anotherLString) {
int len1 = length();
int len2 = anotherLString.length();
int lim = Math.min(len1, len2);
node cn1 = front;
node cn2 = anotherLString.front;
int k = 0;
while (k < lim) {
char c1 = cn1.data;
char c2 = cn2.data;
if (c1 != c2) {
return c1-c2;
}
k++;
cn1 = cn1.next;
cn2 = cn2.next;
}
return len1 - len2;
}
// a boolean equals method that returns true if LString and other are the same, false if not
public boolean equals(Object other) {
if (this == other) {
return true;
}
if (other instanceof LString) {
LString otherLString = (LString)other;
int n = length();
if (n == otherLString.length()) {
node n1 = front;
node n2 = otherLString.front;
while (n1 != null) {
if (n1.data != n2.data) {
return false;
}
n1 = n1.next;
n2 = n2.next;
}
return true;
}
}
return false;
}
// charAt returns the character of LString at the argument index
public char charAt(int index) {
if ((index < 0) || (index >= this.length())) {
throw new IndexOutOfBoundsException();
}
node curNode = front;
for (int i = 0; i < this.length(); i++, curNode = curNode.next) {
if (i == index) {
return curNode.data;
}
}
throw new IllegalStateException();
}
//
public void setCharAt(int index, char ch) {
if (index < 0 || index >= this.length()) {
throw new IndexOutOfBoundsException();
}
else {
node currNode = front;
for (int i = 0; i <this.length(); i++, currNode = currNode.next) {
if (i == index) {
currNode.data = ch;
}
}
}
}
public LString substring(int start, int end) {
if (start < 0 || end > this.length() || start > end) {
throw new IndexOutOfBoundsException();
}
LString substring = new LString();
if (start == end) {
return substring;
}
node node = this.front;
for (int i = 0; i < start; i++) {
node = node.next;
}
node copy = new node(node.data);
substring.front = copy;
for (int i = start+1; i < end; i++) {
node = node.next;
copy = copy.next = new node(node.data);
}
return substring;
}
public LString replace(int start, int end, LString lStr) {
return null;
}
public String toString(){
StringBuilder result = new StringBuilder();
node curr = front;
while (curr != null){
result.append(curr.data);
curr = curr.next;
}
return result.toString();
}
}
一些注意事项:我确实编写了一个 toString()
方法,并且在此代码中还有一个 replace()
方法,我将在此之后编写.
A few notes: I did write a toString()
method, and in this code is also a replace()
method, which I'll write after this.
这是使 end
包含在内的错误和代码:
Here is the error and code for making end
inclusive:
错误:
Running substring tests (63 tests)
Starting tests: E....EEE....E.EEEEEE.....E.EEEEEEE....E.EEEEEEE....E.EEEEEEE...
Time: 0.028
There were 35 failures:
1) test41aSubStringEmpty(LStringTest$LStringSubStringTestSpecial)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTestSpecial.test41aSubStringEmpty(LStringTest.java:368)
... 10 more
2) test43bSubStringOneChar(LStringTest$LStringSubStringTestSpecial)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTestSpecial.test43bSubStringOneChar(LStringTest.java:395)
... 10 more
3) test43cSubStringOneChar(LStringTest$LStringSubStringTestSpecial)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTestSpecial.test43cSubStringOneChar(LStringTest.java:401)
... 10 more
4) test43dSubStringOneCharIsNew(LStringTest$LStringSubStringTestSpecial)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTestSpecial.test43dSubStringOneCharIsNew(LStringTest.java:407)
... 10 more
5) test51bEmptySubstringAtEnd[0](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51bEmptySubstringAtEnd(LStringTest.java:468)
... 10 more
6) test51dSubstringAtStart[0](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not correct expected:<a[]> but was:<a[b]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51dSubstringAtStart(LStringTest.java:478)
... 10 more
7) test51eSubstringAtEnd[0](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51eSubstringAtEnd(LStringTest.java:483)
... 10 more
8) test51fSubstringInMiddle[0](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not correct expected:<[]> but was:<[b]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51fSubstringInMiddle(LStringTest.java:488)
... 10 more
9) test51gSubstringAll[0](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51gSubstringAll(LStringTest.java:493)
... 10 more
10) test51hSubstringAtStartIsNew[0](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not new LString expected:<a[]> but was:<a[b]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51hSubstringAtStartIsNew(LStringTest.java:500)
... 10 more
11) test51jSubstringAtEndIsNew[0](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51jSubstringAtEndIsNew(LStringTest.java:505)
... 10 more
12) test51bEmptySubstringAtEnd[1](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51bEmptySubstringAtEnd(LStringTest.java:468)
... 10 more
13) test51dSubstringAtStart[1](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not correct expected:<a[]> but was:<a[b]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51dSubstringAtStart(LStringTest.java:478)
... 10 more
14) test51eSubstringAtEnd[1](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51eSubstringAtEnd(LStringTest.java:483)
... 10 more
15) test51fSubstringInMiddle[1](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not correct expected:<b[]> but was:<b[c]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51fSubstringInMiddle(LStringTest.java:488)
... 10 more
16) test51gSubstringAll[1](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51gSubstringAll(LStringTest.java:493)
... 10 more
17) test51hSubstringAtStartIsNew[1](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not new LString expected:<a[]> but was:<a[b]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51hSubstringAtStartIsNew(LStringTest.java:500)
... 10 more
18) test51jSubstringAtEndIsNew[1](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51jSubstringAtEndIsNew(LStringTest.java:505)
... 10 more
19) test51kSubstringInMiddleIsNew[1](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not new LString expected:<b[]> but was:<b[c]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51kSubstringInMiddleIsNew(LStringTest.java:515)
... 10 more
20) test51bEmptySubstringAtEnd[2](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51bEmptySubstringAtEnd(LStringTest.java:468)
... 10 more
21) test51dSubstringAtStart[2](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not correct expected:<A long []> but was:<A long [s]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51dSubstringAtStart(LStringTest.java:478)
... 10 more
22) test51eSubstringAtEnd[2](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51eSubstringAtEnd(LStringTest.java:483)
... 10 more
23) test51fSubstringInMiddle[2](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not correct expected:<ng str[]> but was:<ng str[i]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51fSubstringInMiddle(LStringTest.java:488)
... 10 more
24) test51gSubstringAll[2](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51gSubstringAll(LStringTest.java:493)
... 10 more
25) test51hSubstringAtStartIsNew[2](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not new LString expected:<A long []> but was:<A long [s]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51hSubstringAtStartIsNew(LStringTest.java:500)
... 10 more
26) test51jSubstringAtEndIsNew[2](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51jSubstringAtEndIsNew(LStringTest.java:505)
... 10 more
27) test51kSubstringInMiddleIsNew[2](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not new LString expected:<ng str[]> but was:<ng str[i]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51kSubstringInMiddleIsNew(LStringTest.java:515)
... 10 more
28) test51bEmptySubstringAtEnd[3](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51bEmptySubstringAtEnd(LStringTest.java:468)
... 10 more
29) test51dSubstringAtStart[3](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not correct expected:<This is an even[]> but was:<This is an even[ ]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51dSubstringAtStart(LStringTest.java:478)
... 10 more
30) test51eSubstringAtEnd[3](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51eSubstringAtEnd(LStringTest.java:483)
... 10 more
31) test51fSubstringInMiddle[3](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not correct expected:<an even longer[]> but was:<an even longer[ ]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51fSubstringInMiddle(LStringTest.java:488)
... 10 more
32) test51gSubstringAll[3](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51gSubstringAll(LStringTest.java:493)
... 10 more
33) test51hSubstringAtStartIsNew[3](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(0, mid) is not new LString expected:<This is an even[]> but was:<This is an even[ ]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51hSubstringAtStartIsNew(LStringTest.java:500)
... 10 more
34) test51jSubstringAtEndIsNew[3](LStringTest$LStringSubStringTest)
java.lang.IndexOutOfBoundsException
at LString.substring(LString.java:142)
at LStringTest$LStringSubStringTest.test51jSubstringAtEndIsNew(LStringTest.java:505)
... 10 more
35) test51kSubstringInMiddleIsNew[3](LStringTest$LStringSubStringTest)
org.junit.ComparisonFailure: substring(left, right) is not new LString expected:<an even longer[]> but was:<an even longer[ ]>
at org.junit.Assert.assertEquals(Assert.java:115)
at LStringTest$LStringSubStringTest.test51kSubstringInMiddleIsNew(LStringTest.java:515)
... 10 more
Test Failed! (35 of 63 tests failed.)
Test failures: abandoning other phases.
以下是相关的代码差异,仅 substring()
不同:
Here is the relevant differences in code, only substring()
is different:
public LString substring(int start, int end) {
if (start < 0 || end >= this.length() || start > end) {
throw new IndexOutOfBoundsException();
}
LString substring = new LString();
/*if (start == end) {
return substring;
}*/
node node = this.front;
for (int i = 0; i < start; i++) {
node = node.next;
}
node copy = new node(node.data);
substring.front = copy;
for (int i = start; i < end; i++) {
node = node.next;
copy = copy.next = new node(node.data);
}
return substring;
}
关于错误的 LStringTest
部分:
@Test public void test43aSubStringOneChar() {
LString testLString = new LString("a");
assertEquals("Substring of One Character LString is not Empty",
nullLString, testLString.substring(0, 0));
}
@Test public void test43bSubStringOneChar() {
LString testLString = new LString("a");
assertEquals("Substring of One Character LString is not Empty",
nullLString, testLString.substring(1, 1));
}
@Test public void test43cSubStringOneChar() {
LString testLString = new LString("a");
assertEquals("Substring of One Character LString is not equals LString",
testLString, testLString.substring(0, 1));
}
推荐答案
该其他答案中的代码无法编译,即使编译成功,也无法正常工作.
The code in that other answer doesn't compile, and even if it did, doesn't function correctly.
假设您正在使用标准的(对于Java)基于零的索引,并且 end
索引是排他的,则此代码将进行编译和测试.
Assuming you're using standard (for Java) zero-based indexing, and that the end
index is exclusive, this code compiles and is tested.
public LString substring(int start, int end) {
if (start < 0 || end > length() || start > end) {
throw new IndexOutOfBoundsException();
}
LString result = new LString();
if (start == end) {
return result;
}
node node = this.front;
for (int i = 0; i < start; i++) {
node = node.next;
}
node copy = new node(node.data);
result.front = copy;
for (int i = start + 1; i < end; i++) {
node = node.next;
copy = copy.next = new node(node.data);
}
result.size = end - start;
return result;
}
如果您希望 end
包含所有内容,尽管这违反Java约定,则您将更改三件事:
If you wanted end
to be inclusive, though this would be against Java convention, you would change three things:
- 方法开头的保护子句必须说
end> = length()
而不是end>length()
, - 第二个保护子句
if (start == end) { return substring;}
将需要完全删除,并且 - 最后一个for循环将初始化
int i = start
而不是int i = start + 1
.
- the guard clause at the start of the method would have to say
end >= length()
instead ofend > length()
, - the second guard clause
if (start == end) { return substring; }
would need to be removed entirely, and - the last for loop would initialize
int i = start
instead ofint i = start + 1
.
顺便说一句,如果您在类中具有 toString()
方法,则更容易查看您的 LString
实例发生了什么.
By the way, it's much easier to see what's happening with your LString
instances if you have a toString()
method in the class.
@Override
public String toString() {
if (this.front == null) return "";
StringBuilder sb = new StringBuilder(length());
node node = this.front;
do sb.append(node.data);
while ((node = node.next) != null);
return sb.toString();
}
这篇关于链表对象的substring()方法的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!