jdk类库源码分析-StringBuffer、StringBuilder

末蓝、 2022-07-13 22:39 125阅读 0赞

**StringBuffer源码分析**  
这里主要是拿出一些常用方法的分析，StringBuffer中很多的方法都使用Synchronized关键字修饰，所以是线程安全的。

package java.lang;
    
    public final class StringBuffer extends AbstractStringBuilder implements java.io.Serializable, CharSequence { 
    
        static final long serialVersionUID = 3388685877147921107L;
    
        /* * 默认大小是16 */
        public StringBuffer() {
            super(16);
        }
    
        /* * 创建capacity大小的StringBuffer的对象 */
        public StringBuffer(int capacity) {
            super(capacity);
        }
    
        /* * String类型 字符串转为StringBuffer类型，字符串大小扩大16 */
        public StringBuffer(String str) {
            super(str.length() + 16);
            append(str);
        }
    
        /* * 返回字符串长度,使用synchronized同步关键字修饰，线程安全 */
        public synchronized int length() {
            return count;
        }
    
        /* * 返回字符串数组大小,使用synchronized同步关键字修饰，线程安全 */
        public synchronized int capacity() {
            return value.length;
        }
    
        /* * 返回指定索引处的字符,使用synchronized同步关键字修饰，线程安全 */
        public synchronized char charAt(int index) {
            if ((index < 0) || (index >= count))
                throw new StringIndexOutOfBoundsException(index);
            return value[index];
        }
    
        /* * 把Object对象转为字符串添加进目标对象 */
        public synchronized StringBuffer append(Object obj) {
            super.append(String.valueOf(obj));
            return this;
        }
    
        /* * 把String类型字符串添加到目标对象 * * @see java.lang.AbstractStringBuilder#append(java.lang.String) */
        public synchronized StringBuffer append(String str) {
            super.append(str);
            return this;
        }
    
        /* * StringBuffer类型字符串添加到目标对象(non-Javadoc) * * @see java.lang.AbstractStringBuilder#append(java.lang.StringBuffer) */
        public synchronized StringBuffer append(StringBuffer sb) {
            super.append(sb);
            return this;
        }
    
        /* * 调用的String类型的toString方法(non-Javadoc) * * @see java.lang.AbstractStringBuilder#toString() */
        public synchronized String toString() {
            return new String(value, 0, count);
        }
        /* * 把Object对象插入目标字符串，调用父类的insert方法，下面贴出父类的insert方法non-Javadoc) * @see java.lang.AbstractStringBuilder#insert(int, java.lang.Object) */
        public synchronized StringBuffer insert(int offset, Object obj) {
            super.insert(offset, String.valueOf(obj));
            return this;
        }
    
        /* * (non-Javadoc) * 这个方法在StringBuffer类中经常调用这里贴出来参考 * @see java.lang.AbstractStringBuilder#insert(int, char[], int, int) */
        public AbstractStringBuilder insert(int index, char[] str, int offset,
                int len) {
            if ((index < 0) || (index > length()))
                throw new StringIndexOutOfBoundsException(index);
            if ((offset < 0) || (len < 0) || (offset > str.length - len))
                throw new StringIndexOutOfBoundsException("offset " + offset
                        + ", len " + len + ", str.length " + str.length);
            ensureCapacityInternal(count + len);
            System.arraycopy(value, index, value, index + len, count - index);
            System.arraycopy(str, offset, value, index, len);
            count += len;
            return this;
        }
    }

**StringBuilder源码分析**

package java.lang;
    
    
    public final class StringBuilder extends AbstractStringBuilder implements java.io.Serializable, CharSequence { 
    
        /** use serialVersionUID for interoperability */
        static final long serialVersionUID = 4383685877147921099L;
    
        /** * 默认大小16 */
        public StringBuilder() {
            super(16);
        }
    
       /* * 创建自定capacity大小的StringBuilder的字符串 */
        public StringBuilder(int capacity) {
            super(capacity);
        }
        /* * 把String类型字符串转为StringBuilder类型的字符串 */
        public StringBuilder(String str) {
            super(str.length() + 16);
            append(str);
        }
        /* * 把Object对象添加到目标对象(non-Javadoc) * @see java.lang.AbstractStringBuilder#append(java.lang.Object) */
        public StringBuilder append(Object obj) {
            return append(String.valueOf(obj));
        }
       /* * 调用父类的delete方法，下面贴出来父类的方法(non-Javadoc) * @see java.lang.AbstractStringBuilder#delete(int, int) */
    
    
        public StringBuilder delete(int start, int end) {
            super.delete(start, end);
            return this;
        }
     /** * 指定删除的字符 */
        public AbstractStringBuilder delete(int start, int end) {
            if (start < 0)
                throw new StringIndexOutOfBoundsException(start);
            if (end > count)
                end = count;
            if (start > end)
                throw new StringIndexOutOfBoundsException();
            int len = end - start;
            if (len > 0) {
                System.arraycopy(value, start+len, value, start, count-end);
                count -= len;
            }
            return this;
        }
    
    }