数字与字符串系列教材 （十）- 自己开发一个Java StringBuffer

StringBuffer第二道练习题答案

步骤1:IStringBuffer接口
步骤2:value和capacity
步骤3:带参构造方法
步骤4:反转 reverse
步骤5:插入insert 和 append
步骤6:删除 delete
步骤7:练习-性能比较
步骤8:答案-性能比较

步骤 1 : IStringBuffer接口

package character;

  

public interface IStringBuffer {

    public void append(String str); //追加字符串 

    public void append(char c);  //追加字符

    public void insert(int pos,char b); //指定位置插入字符

    public void insert(int pos,String b); //指定位置插入字符串

    public void delete(int start); //从开始位置删除剩下的

    public void delete(int start,int end); //从开始位置删除结束位置-1

    public void reverse(); //反转

    public int length(); //返回长度

}

步骤 2 : value和capacity

value：用于存放字符数组
capacity： 容量
无参构造方法： 根据容量初始化value

public MyStringBuffer(){

    value = new char[capacity];

}

package character;

public class MyStringBuffer implements IStringBuffer{

    int capacity = 16;

    int length = 0;

    char[] value;

    public MyStringBuffer(){

        value = new char[capacity];

    }

     

    @Override

    public void append(String str) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void append(char c) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void insert(int pos, char b) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void delete(int start) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void delete(int start, int end) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void reverse() {

        // TODO Auto-generated method stub

         

    }

    @Override

    public int length() {

        // TODO Auto-generated method stub

        return 0;

    }

}

步骤 3 : 带参构造方法

package character;

public class MyStringBuffer implements IStringBuffer{

    int capacity = 16;

    int length = 0;

    char[] value;

    public MyStringBuffer(){

        value = new char[capacity];

    }

     

    //有参构造方法

    public MyStringBuffer(String str){

        if(null!=str)

            value =str.toCharArray();

         

        length = value.length;

         

        if(capacity<value.length)

            capacity  = value.length*2;

    }

     

    @Override

    public void append(String str) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void append(char c) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void insert(int pos, char b) {

    }

    @Override

    public void delete(int start) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void delete(int start, int end) {

        // TODO Auto-generated method stub

         

    }

    @Override

    public void reverse() {

        // TODO Auto-generated method stub

         

    }

    @Override

    public int length() {

        // TODO Auto-generated method stub

        return length;

    }

    @Override

    public void insert(int pos, String b) {

    }

}

步骤 4 : 反转 reverse

package character;

public class MyStringBuffer implements IStringBuffer {

    int capacity = 16;

    int length = 0;

    char[] value;

    public MyStringBuffer() {

        value = new char[capacity];

    }

    // 有参构造方法

    public MyStringBuffer(String str) {

        this();

        if (null == str)

            return;

        if (capacity < str.length()) {

            capacity = value.length * 2;

            value = new char[capacity];

        }

        if (capacity >= str.length())

            System.arraycopy(str.toCharArray(), 0, value, 0, str.length());

        length = str.length();

    }

    @Override

    public void reverse() {

        for (int i = 0; i < length / 2; i++) {

            char temp = value[i];

            value[i] = value[length - i - 1];

            value[length - i - 1] = temp;

        }

    }

    @Override

    public void append(String str) {

        // TODO Auto-generated method stub

    }

    @Override

    public void append(char c) {

        // TODO Auto-generated method stub

    }

    @Override

    public void insert(int pos, char b) {

        // TODO Auto-generated method stub

    }

    @Override

    public void insert(int pos, String b) {

        // TODO Auto-generated method stub

    }

    @Override

    public void delete(int start) {

        // TODO Auto-generated method stub

    }

    @Override

    public void delete(int start, int end) {

        // TODO Auto-generated method stub

    }

    @Override

    public int length() {

        // TODO Auto-generated method stub

        return length;

    }

    public String toString() {

        char[] realValue = new char[length];

        System.arraycopy(value, 0, realValue, 0, length);

        return new String(realValue);

    }

    public static void main(String[] args) {

        MyStringBuffer sb = new MyStringBuffer("there light");

        sb.reverse();

        System.out.println(sb);

    }

}

步骤 5 : 插入insert 和 append

边界条件判断
插入之前，首先要判断的是一些边界条件。 比如插入位置是否合法，插入的字符串是否为空

扩容
1. 要判断是否需要扩容。 如果插入的字符串加上已经存在的内容的总长度超过了容量，那么就需要扩容。
2. 数组的长度是固定的，不能改变的，数组本身不支持扩容。 我们使用变通的方式来解决这个问题。
3. 根据需要插入的字符串的长度和已经存在的内容的长度，计算出一个新的容量。 然后根据这个容量，创建一个新的数组，接着把原来的数组的内容，复制到这个新的数组中来。并且让value这个引用，指向新的数组，从而达到扩容的效果。

插入字符串
1. 找到要插入字符串的位置，从这个位置开始，把原数据看成两段，把后半段向后挪动一个距离，这个距离刚好是插入字符串的长度
2. 然后把要插入的数据，插入这个挪出来的，刚刚好的位置里。

修改length的值
最后修改length的值，是原来的值加上插入字符串的长度

insert(int, char)
参数是字符的insert方法，通过调用insert(int, String) 也就实现了。

append
追加，就是在最后位置插入。 所以不需要单独开发方法，直接调用insert方法，就能达到最后位置插入的效果

package character;

  

public class MyStringBuffer implements IStringBuffer{

  

    int capacity = 16;

    int length = 0;

    char[] value;

    public MyStringBuffer(){

        value = new char[capacity];

    }

      

    //有参构造方法

    public MyStringBuffer(String str){

        this();

        if(null==str)

            return;

          

        if(capacity<str.length()){

            capacity  = value.length*2;

            value=new char[capacity];

        }

          

        if(capacity>=str.length())

            System.arraycopy(str.toCharArray(), 0, value, 0, str.length());

          

        length = str.length();

          

    }

      

    @Override

    public void append(String str) {

        insert(length,str);

    }

  

    @Override

    public void append(char c) {

        append(String.valueOf(c));

          

    }

  

    @Override

    public void insert(int pos, char b) {

        insert(pos,String.valueOf(b));

    }

  

    @Override

    public void delete(int start) {

        // TODO Auto-generated method stub

          

    }

  

    @Override

    public void delete(int start, int end) {

        // TODO Auto-generated method stub

          

    }

  

    @Override

    public void reverse() {

        for (int i = 0; i < length/2; i++) {

            char temp = value[i];

            value[i] = value[length-i-1];

            value[length-i-1] = temp;

        }

    }

  

    @Override

    public int length() {

        // TODO Auto-generated method stub

        return length;

    }

  

    @Override

    public void insert(int pos, String b) {

  

        //边界条件判断

        if(pos<0)

            return;

          

        if(pos>length)

            return;

          

        if(null==b)

            return;

          

        //扩容

        while(length+b.length()>capacity){

            capacity = (int) ((length+b.length())*1.5f);

            char[] newValue = new char[capacity];

            System.arraycopy(value, 0, newValue, 0, length);

            value = newValue;

        }

          

        char[] cs = b.toCharArray();

          

        //先把已经存在的数据往后移

          

        System.arraycopy(value, pos, value,pos+ cs.length, length-pos);

        //把要插入的数据插入到指定位置

        System.arraycopy(cs, 0, value, pos, cs.length);

          

        length = length+cs.length;

          

    }

      

    public String toString(){

          

        char[] realValue = new char[length];

  

        System.arraycopy(value, 0, realValue, 0, length);

          

        return new String(realValue);

          

    }

      

    public static void main(String[] args) {

        MyStringBuffer sb = new MyStringBuffer("there light");

        System.out.println(sb);

        sb.insert(0, "let ");

        System.out.println(sb);

  

        sb.insert(10, "be ");

        System.out.println(sb);

        sb.insert(0, "God Say:");

        System.out.println(sb);

        sb.append("!");

        System.out.println(sb);

        sb.append('?');

        System.out.println(sb);

        sb.reverse();

        System.out.println(sb);

          

    }

  

}

步骤 6 : 删除 delete

package character;

public class MyStringBuffer implements IStringBuffer{

    int capacity = 16;

    int length = 0;

    char[] value;

    public MyStringBuffer(){

        value = new char[capacity];

    }

     

    //有参构造方法

    public MyStringBuffer(String str){

        this();

        if(null==str)

            return;

         

        if(capacity<str.length()){

            capacity  = value.length*2;

            value=new char[capacity];

        }

         

        if(capacity>=str.length())

            System.arraycopy(str.toCharArray(), 0, value, 0, str.length());

         

        length = str.length();

         

    }

     

    @Override

    public void append(String str) {

        insert(length,str);

    }

    @Override

    public void append(char c) {

        append(String.valueOf(c));

         

    }

    @Override

    public void insert(int pos, char b) {

        insert(pos,String.valueOf(b));

    }

    @Override

    public void delete(int start) {

         

        delete(start,length);

    }

    @Override

    public void delete(int start, int end) {

        //边界条件判断

        if(start<0)

            return;

         

        if(start>length)

            return;

         

        if(end<0)

            return;

         

        if(end>length)

            return;

         

        if(start>=end)

            return;

         

        System.arraycopy(value, end, value, start, length- end);

        length-=end-start;

         

    }

    @Override

    public void reverse() {

        for (int i = 0; i < length/2; i++) {

             

            char temp = value[i];

            value[i] = value[length-i-1];

            value[length-i-1] = temp;

        }

         

    }

    @Override

    public int length() {

        // TODO Auto-generated method stub

        return length;

    }

    @Override

    public void insert(int pos, String b) {

        //边界条件判断

        if(pos<0)

            return;

         

        if(pos>length)

            return;

         

        if(null==b)

            return;

         

        //扩容

        while(length+b.length()>capacity){

            capacity = (int) ((length+b.length())*1.5f);

            char[] newValue = new char[capacity];

            System.arraycopy(value, 0, newValue, 0, length);

            value = newValue;

        }

         

        char[] cs = b.toCharArray();

         

        //先把已经存在的数据往后移

         

        System.arraycopy(value, pos, value,pos+ cs.length, length-pos);

        //把要插入的数据插入到指定位置

        System.arraycopy(cs, 0, value, pos, cs.length);

         

        length = length+cs.length;

         

    }

     

    public String toString(){

         

        char[] realValue = new char[length];

        System.arraycopy(value, 0, realValue, 0, length);

         

        return new String(realValue);

         

    }

     

    public static void main(String[] args) {

        MyStringBuffer sb = new MyStringBuffer("there light");

        System.out.println(sb);

        sb.insert(0, "let ");

        System.out.println(sb);

        sb.insert(10, "be ");

        System.out.println(sb);

        sb.insert(0, "God Say:");

        System.out.println(sb);

        sb.append("!");

        System.out.println(sb);

        sb.append('?');

        System.out.println(sb);

        sb.reverse();

        System.out.println(sb);

         

        sb.reverse();

        System.out.println(sb);

         

        sb.delete(0,4);

        System.out.println(sb);

        sb.delete(4);

        System.out.println(sb);

    }

}

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