由于前面学习了StringBuffer和StringBuilder的父类AbstractStringBuilder,他们俩的很多方法都是直接super了父类的,也为了较好的比较StringBuffer和StringBuilder,所以把二者放在同一博文中。
一.StringBuffer
1.静态类,不能被继承,实现了Serializable和CharSequence接口。
public final class StringBuffer extends AbstractStringBuilder implements java.io.Serializable, CharSequence2.构造函数
public StringBuffer() {//StringBuffer的默认 容量 是16,注意是容量不是长度 super(16); } public StringBuffer(int capacity) {//也可以在初始化StringBuffer时为它指定容量,为了减少不必要的扩容,尽量在初始化StringBuffer时指定 容量 super(capacity); } public StringBuffer(String str) {//若初始化StringBuffer时传入字符串,则 容量 为字符串长度+默认容量16 super(str.length() + 16); append(str); } public StringBuffer(CharSequence seq) { this(seq.length() + 16); append(seq); }3.成员函数
方法大部分都定义为synchronized,这是StringBuffer和StringBuilder的最大区别,也就是StringBuffer是同步的,线程安全的,而StringBuilder是非线程安全的。当然嘛,上帝给你关了一扇门总是会为你开一扇窗的,StringBuffer是线程安全的但是效率上去略逊与StringBuilder.
由于几乎都是super的父类的,故不再累述,见我的前一篇JDK源码学习----AbstractStringBuilder http://blog.csdn.net/sheepmu/article/details/26095203
public synchronized int length() { return count; } public synchronized int capacity() { return value.length; } public synchronized void ensureCapacity(int minimumCapacity) { if (minimumCapacity > value.length) { expandCapacity(minimumCapacity); } } public synchronized void trimToSize() { super.trimToSize(); } public synchronized void setLength(int newLength) { super.setLength(newLength); } public synchronized char charAt(int index) { if ((index < 0) || (index >= count)) throw new StringIndexOutOfBoundsException(index); return value[index]; } public synchronized StringBuffer append(Object obj) { super.append(String.valueOf(obj)); return this; } public synchronized StringBuffer append(String str) { super.append(str); return this; } public synchronized StringBuffer append(StringBuffer sb) { super.append(sb); 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()); } public synchronized StringBuffer delete(int start, int end) { super.delete(start, end); return this; } public synchronized StringBuffer deleteCharAt(int index) { super.deleteCharAt(index); return this; } public synchronized String substring(int start) { return substring(start, count); } public int indexOf(String str) { return indexOf(str, 0); } public synchronized int indexOf(String str, int fromIndex) { return String.indexOf(value, 0, count, str.toCharArray(), 0, str.length(), fromIndex); } public synchronized StringBuffer reverse() { super.reverse(); return this; } public synchronized String toString() { return new String(value, 0, count); } private static final java.io.ObjectStreamField[] serialPersistentFields = { new java.io.ObjectStreamField("value", char[].class), new java.io.ObjectStreamField("count", Integer.TYPE), new java.io.ObjectStreamField("shared", Boolean.TYPE), }; 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(); } 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 = (int)fields.get("count", 0); } }二.StringBuilder
1.静态类,不能被继承,实现了Serializable和CharSequence接口。 (同StringBuffer)
public final class StringBuilder extends AbstractStringBuilder implements java.io.Serializable, CharSequence2.构造函数 (同StringBuffer)
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); }3.成员函数 (与StringBuffer最大的区别就是非同步的)
public StringBuilder append(Object obj) { return append(String.valueOf(obj)); } public StringBuilder append(String str) { super.append(str); return this; } private StringBuilder append(StringBuilder sb) { if (sb == null) return append("null"); int len = sb.length(); int newcount = count + len; if (newcount > value.length) expandCapacity(newcount); sb.getChars(0, len, value, count); count = newcount; return this; } public StringBuilder append(StringBuffer sb) { super.append(sb); return this; } public StringBuilder append(CharSequence s) { if (s == null) s = "null"; if (s instanceof String) return this.append((String)s); if (s instanceof StringBuffer) return this.append((StringBuffer)s); if (s instanceof StringBuilder) return this.append((StringBuilder)s); return this.append(s, 0, s.length()); } public StringBuilder delete(int start, int end) { super.delete(start, end); return this; } public StringBuilder deleteCharAt(int index) { super.deleteCharAt(index); return this; } public StringBuilder insert(int index, char str[], int offset, int len) { super.insert(index, str, offset, len); return this; } public int indexOf(String str) { return indexOf(str, 0); } public int indexOf(String str, int fromIndex) { return String.indexOf(value, 0, count, str.toCharArray(), 0, str.length(), fromIndex); } public int lastIndexOf(String str) { return lastIndexOf(str, count); } public StringBuilder reverse() { super.reverse(); return this; } public String toString() { // Create a copy, don't share the array return new String(value, 0, count); }
JDK源码学习----StringBuffer+StringBuilder,布布扣,bubuko.com
JDK源码学习----StringBuffer+StringBuilder
原文地址:http://blog.csdn.net/sheepmu/article/details/27123541