java.lang.*中StringBuffer 源代码详解

野性酷女 2022-11-27 03:11 187阅读 0赞

### java.lang.\*中StringBuffer 源代码详解 ###

*   *  核心方法
     *  StringBuffer()构造方法
     *  synchronized int length()
     *  synchronized int capacity()
     *  synchronized char charAt()
     *  synchronized void setCharAt()
     *  synchronized StringBuffer insert()
     *  int indexOf()
     *  int lastIndexOf()
     *  synchronized String toString()
     *  synchronized void writeObject()
     *  void readObject()

## 核心方法 ##

public final class StringBuffer extends AbstractStringBuilder implements java.io.Serializable, CharSequence
    
    StringBuffer()构造方法[OK]
    synchronized int length() 实际存在的字符长度[OK]
    synchronized int capacity() 容量的长度[OK]
    synchronized char charAt() 返回指定索引位置的字符[OK]
    synchronized void setCharAt() 设置指定索引位置的字符[OK]
    synchronized StringBuffer insert() 往指定索引位置插入对象[OK]
    int indexOf() 获取字符的索引位置[OK]
    int lastIndexOf() 逆序检索字符的索引位置[OK]
    synchronized String toString() 获取字符串对象[OK]
    synchronized void writeObject() 序列化写入数据[OK]
    void readObject() 反序列化,读取数据[OK]

## StringBuffer()构造方法 ##

public StringBuffer() { 
        super(16);//默认容量大小为16
    }
    
    public StringBuffer(int capacity) { 
        super(capacity);//指定容量大小
    }
    
    public StringBuffer(String str) { 
        super(str.length() + 16);//默认初始化容量str.length + 16
        append(str);
    }
    
    public StringBuffer(CharSequence seq) { 
        this(seq.length() + 16);//默认初始化容量str.length + 16
        append(seq);
    }

## synchronized int length() ##

public synchronized int length() { 
        return count;//实际存在的字符长度
    }

## synchronized int capacity() ##

public synchronized int capacity() { 
        return value.length;//容量的长度
    }

## synchronized char charAt() ##

/** * 返回指定索引位置的字符 * @param index 索引位置 */
    public synchronized char charAt(int index) { 
    	//判断角标是否越界
        if ((index < 0) || (index >= count))
            throw new StringIndexOutOfBoundsException(index);
        return value[index];
    }

## synchronized void setCharAt() ##

/** * 设置某个索引位置的字符 * @param index 索引位置 * @param ch 替换的字符 */
    public synchronized void setCharAt(int index, char ch) { 
    	//判断角标是否越界
        if ((index < 0) || (index >= count))
            throw new StringIndexOutOfBoundsException(index);
        toStringCache = null;
        value[index] = ch;
    }

## synchronized StringBuffer insert() ##

public synchronized StringBuffer insert(int index, char[] str, int offset,
                                                int len)
    { 
        toStringCache = null;
        super.insert(index, str, offset, len);
        return this;
    }
    
    public synchronized StringBuffer insert(int offset, Object obj) { 
        toStringCache = null;
        super.insert(offset, String.valueOf(obj));
        return this;
    }
    
    public synchronized StringBuffer insert(int offset, String str) { 
        toStringCache = null;
        super.insert(offset, str);
        return this;
    }
    
    public synchronized StringBuffer insert(int offset, char[] str) { 
        toStringCache = null;
        super.insert(offset, str);
        return this;
    }
    
    public StringBuffer insert(int dstOffset, CharSequence s) { 
        // Note, synchronization achieved via invocations of other StringBuffer methods
        // after narrowing of s to specific type
        // Ditto for toStringCache clearing
        super.insert(dstOffset, s);
        return this;
    }
    
    public synchronized StringBuffer insert(int dstOffset, CharSequence s,
                int start, int end)
    { 
        toStringCache = null;
        super.insert(dstOffset, s, start, end);
        return this;
    }
    
    public  StringBuffer insert(int offset, boolean b) { 
        // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
        // after conversion of b to String by super class method
        // Ditto for toStringCache clearing
        super.insert(offset, b);
        return this;
    }
    
    public synchronized StringBuffer insert(int offset, char c) { 
        toStringCache = null;
        super.insert(offset, c);
        return this;
    }
    
    public StringBuffer insert(int offset, int i) { 
        // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
        // after conversion of i to String by super class method
        // Ditto for toStringCache clearing
        super.insert(offset, i);
        return this;
    }
    
    public StringBuffer insert(int offset, long l) { 
        // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
        // after conversion of l to String by super class method
        // Ditto for toStringCache clearing
        super.insert(offset, l);
        return this;
    }
    
    public StringBuffer insert(int offset, float f) { 
        // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
        // after conversion of f to String by super class method
        // Ditto for toStringCache clearing
        super.insert(offset, f);
        return this;
    }
    
    public StringBuffer insert(int offset, double d) { 
        // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
        // after conversion of d to String by super class method
        // Ditto for toStringCache clearing
        super.insert(offset, d);
        return this;
    }

## int indexOf() ##

public int indexOf(String str) { 
        // Note, synchronization achieved via invocations of otherStringBuffer methods
        return super.indexOf(str);
    }
    
    public synchronized int indexOf(String str, int fromIndex) { 
        return super.indexOf(str, fromIndex);
    }

## int lastIndexOf() ##

public int lastIndexOf(String str) { 
        // Note, synchronization achieved via invocations of other StringBuffer methods
        return lastIndexOf(str, count);
    }
    
    public synchronized int lastIndexOf(String str, int fromIndex) { 
        return super.lastIndexOf(str, fromIndex);
    }

## synchronized String toString() ##

public synchronized String toString() { 
    	//如果缓存为空,重新进行拷贝
        if (toStringCache == null) { 
        	//toStringCache会缓存最后一次toString的值
        	//只有当内部内容被修改的情况下,会将其清空
            toStringCache = Arrays.copyOfRange(value, 0, count);
        }
        return new String(toStringCache, true);
    }

## synchronized void writeObject() ##

/** * 序列化写入数据 */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
            throws java.io.IOException { 
        java.io.ObjectOutputStream.PutField fields = s.putFields();
        fields.put("value", value);
        fields.put("count", count);
        fields.put("shared", false);
        s.writeFields();
    }

## void readObject() ##

/** * 反序列化,读取数据 */
    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException { 
        java.io.ObjectInputStream.GetField fields = s.readFields();
        value = (char[])fields.get("value", null);
        count = fields.get("count", 0);
    }

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