LString类，用链表做琴弦，JAVA

我无法写一个compareTo()和charAt()方法是建立一个字符串链表对象。类，称为LString包含一个构造函数和其他一些方法。它运行与测试其能力，作为一个链表字符串生成另一个文件，我收到此错误信息：LString类，用链表做琴弦，JAVA

Running constructor, length, toString tests (10 tests) 
Starting tests: .......... 
Time: 0.000 
OK! (10 tests passed.) 

Running compareTo and equals tests (18 tests) 
Starting tests: EEEEEEEE.EEE.E.... 
Time: 0.016 

There were 12 failures: 
1) t21aTestCompareTo[0](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: compareTo of "abc" and "abd" wrong expected:<-1> but was:<0> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at org.junit.Assert.assertEquals(Assert.java:555) 
     at LStringTest$LStringCompareToTest.t21aTestCompareTo(LStringTest.java:259) 
     ... 9 more 
2) t22aTestEquals[0](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: equals of "abc" and "abd" wrong expected:<false> but was:<true> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 
3) t21aTestCompareTo[1](LStringTest$LStringCompareToTest) 
java.lang.IndexOutOfBoundsException: bad index 
     at LString.charAt(LString.java:91) 
     at LString.compareTo(LString.java:64) 
     at LStringTest$LStringCompareToTest.t21aTestCompareTo(LStringTest.java:259) 
     ... 9 more 
4) t22aTestEquals[1](LStringTest$LStringCompareToTest) 
java.lang.NullPointerException 
     at LString.equals(LString.java:79) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 
5) t21aTestCompareTo[2](LStringTest$LStringCompareToTest) 
java.lang.IndexOutOfBoundsException: bad index 
     at LString.charAt(LString.java:91) 
     at LString.compareTo(LString.java:64) 
     at LStringTest$LStringCompareToTest.t21aTestCompareTo(LStringTest.java:259) 
     ... 9 more 
6) t22aTestEquals[2](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: equals of "a" and "ab" wrong expected:<false> but was:<true> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 
7) t21aTestCompareTo[3](LStringTest$LStringCompareToTest) 
java.lang.IndexOutOfBoundsException: bad index 
     at LString.charAt(LString.java:91) 
     at LString.compareTo(LString.java:64) 
     at LStringTest$LStringCompareToTest.t21aTestCompareTo(LStringTest.java:259) 
     ... 9 more 
8) t22aTestEquals[3](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: equals of "abc" and "abcd" wrong expected:<false> but was:<true> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 
9) t22aTestEquals[4](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: equals of "B" and "a" wrong expected:<false> but was:<true> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 
10) t21aTestCompareTo[5](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: compareTo of "BB" and "Ba" wrong expected:<-1> but was:<0> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at org.junit.Assert.assertEquals(Assert.java:555) 
     at LStringTest$LStringCompareToTest.t21aTestCompareTo(LStringTest.java:259) 
     ... 9 more 
11) t22aTestEquals[5](LStringTest$LStringCompareToTest) 
java.lang.AssertionError: equals of "BB" and "Ba" wrong expected:<false> but was:<true> 
     at org.junit.Assert.fail(Assert.java:88) 
     at org.junit.Assert.failNotEquals(Assert.java:743) 
     at org.junit.Assert.assertEquals(Assert.java:118) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 
12) t22aTestEquals[6](LStringTest$LStringCompareToTest) 
java.lang.NullPointerException 
     at LString.equals(LString.java:79) 
     at LStringTest$LStringCompareToTest.t22aTestEquals(LStringTest.java:269) 
     ... 9 more 

Test Failed! (12 of 18 tests failed.) 

Test failures: abandoning other phases.

的LString类是为了模仿Java的String和StringBuilder，但链表而不是阵列。我对如何使用this关键字有点困惑。在下面的compareTo()方法中，我想象使用this通过对自己说：“如果此索引处的此LStrings字符等于同一索引处的参数的LString字符，则返回0.”

我引用此页面，但不能确定如何将其有效地写：http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#compareTo%28java.lang.String%29

我想compareTo()返回0，如果LStrings有相同的字符，值小于零，如果这LString排在最后少而不是另一个字符串，如果按字典顺序更大，则其值大于零。

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 != ""){ 

       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 total = 0; 
     for (int i = 0; i < anotherLString.length(); i++) { 
     total += this.charAt(i) - anotherLString.charAt(i); 
     } 
     return total; 

     //} 
     //return this.length()-anotherLString.length(); 
    } 

    // a boolean equals method that returns true if LString and other are the same, false if not 
    public boolean equals(Object other) { 
     if (other == null || !(other instanceof LString)) { 
      return false; 
     } 
     else { 
      LString otherLString = (LString)other; 
     if (this.front.data == otherLString.front.data) { 

       return true; 
     } 
     } 
     return true; 
    } 

    // charAt returns the character of LString at the argument index 
    public char charAt(int index) { 

     if ((index < 0) || (index >= this.length())) { 
     throw new IndexOutOfBoundsException("bad index"); 
     } 
     return this.front.data; 
    }

此代码中未完成相关方法。任何意见，赞赏，试图学习Java。

来源

2015-03-03 boop

只是FYI你comapreTo方法将抛出一个空指针异常，如果'anotherString'比哪种方法被称为 – Vihar 2015-03-03 05:07:33

我稍微纠正你的代码。

如果您定义了equals()，则应该定义hashCode()。同样是非常有用的实施LString为CharSequence的。

public class LString implements Comparable<LString> 
{ 
    Node front; 
    int size; 

    //Creating a node class 
    private static 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); 
     // char v1 = front.data; 
     // char v2 = anotherLString.front.data; 
     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 anotherLString = (LString) other; 
      int n = length(); 
      if (n == anotherLString.length()) 
      { 
       Node n1 = front; 
       Node n2 = anotherLString.front; 
       while (n1 != null) 
       { 
        if (n1.data != n2.data) 
        { 
         return false; 
        } 
       } 

       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("bad index"); 
     } 

     Node curNode = front; 
     for (int i = 0; i < this.length(); i++, curNode = curNode.next) 
     { 
      if (i == index) 
      { 
       return curNode.data; 
      } 
     } 

     throw new IllegalStateException(); 
    } 
}

来源

2015-03-03 07:10:51

此外串大，则可能需要重写toString（）方法 – 2015-03-03 13:56:54

LString类，用链表做琴弦，JAVA

回答

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