【源码】StringBuilder和StringBuffer源码深度剖析

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我觉得要通过源码研究一个类，应该先从整体上了解这个类，比如说这个类的继承体系，有哪些超类，继承了那些接口，提供了什么样的方法。然后，我们再去源码中了解具体的实现过程，这样才不会乱~

我们来看看StringBuilder和StringBuffer的继承关系:

public final class StringBuilder//1.5开始
    extends AbstractStringBuilder
    implements java.io.Serializable, CharSequence

public final class StringBuffer//1.0就有了
    extends AbstractStringBuilder
    implements java.io.Serializable, CharSequence  

package java.lang;

/**
 * @author Mike McCloskey
 * @since 1.4
 * @spec JSR-51
 */
public interface CharSequence {
    int length();
    char charAt(int index);
    CharSequence subSequence(int start, int end);
    public String toString();
}

abstract class AbstractStringBuilder implements Appendable, CharSequence

package java.lang;
import java.io.IOException;
public interface Appendable {
    Appendable append(CharSequence csq) throws IOException;
    Appendable append(CharSequence csq, int start, int end) throws IOException;
    Appendable append(char c) throws IOException;
}

/**
     * The value is used for character storage.
     */
    char[] value;//用于存放字符的数组
    /**
     * The count is the number of characters used.
     */
    int count;//当前字符总数

 AbstractStringBuilder() {}
    AbstractStringBuilder(int capacity) {
        value = new char[capacity];
    }

public void ensureCapacity(int minimumCapacity) {
        if (minimumCapacity > 0)
            ensureCapacityInternal(minimumCapacity);
    }
    /**
     * This method has the same contract as ensureCapacity, but is
     * never synchronized.
     */
    private void ensureCapacityInternal(int minimumCapacity) {
        // overflow-conscious code
        if (minimumCapacity - value.length > 0)
            expandCapacity(minimumCapacity);
    }
    /**
     * This implements the expansion semantics of ensureCapacity with no
     * size check or synchronization.
     */
    void expandCapacity(int minimumCapacity) {
        int newCapacity = value.length * 2 + 2;
        if (newCapacity - minimumCapacity < 0)
            newCapacity = minimumCapacity;
        if (newCapacity < 0) {
            if (minimumCapacity < 0) // overflow
                throw new OutOfMemoryError();
            newCapacity = Integer.MAX_VALUE;
        }
        value = Arrays.copyOf(value, newCapacity);
    }

  public AbstractStringBuilder append(String str) {
        if (str == null) str = "null";
        int len = str.length();
        ensureCapacityInternal(count + len);
        str.getChars(0, len, value, count);
        count += len;
        return this;
    }

public void trimToSize() {
        if (count < value.length) {
            value = Arrays.copyOf(value, count);
        }
    }

  public StringBuilder() {
        super(16);
    }

    public StringBuilder(int capacity) {
        super(capacity);
    }
    public StringBuilder(String str) {
        super(str.length() + 16);
        append(str);
    }

    public StringBuilder(CharSequence seq) {
        this(seq.length() + 16);
        append(seq);
    }

 public StringBuilder append(Object obj) {
        return append(String.valueOf(obj));
    }
    public StringBuilder append(String str) {
        super.append(str);
        return this;
    }

 public String toString() {
        // Create a copy, don't share the array
        return new String(value, 0, count);
    }

  private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
        s.writeInt(count);
        s.writeObject(value);
    }
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();
        count = s.readInt();
        value = (char[]) s.readObject();
    }

public synchronized int length() {
        return count;
    }
public synchronized void trimToSize() {
        super.trimToSize();
    }
 public synchronized StringBuffer append(String str) {
        super.append(str);
        return this;
    }

public StringBuffer append(CharSequence s) {
        // Note, synchronization achieved via other invocations
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.append((String)s);
        if (s instanceof StringBuffer)
            return this.append((StringBuffer)s);
        return this.append(s, 0, s.length());
    }

【源码】StringBuilder和StringBuffer源码深度剖析,布布扣,bubuko.com

【源码】StringBuilder和StringBuffer源码深度剖析

标签：style   blog   http   color   java   使用   os   io   

原文地址：http://blog.csdn.net/chdjj/article/details/38407329