深入学习java源码之CharSequence.chars()CharSequence.codePoints()
原创
©著作权归作者所有：来自51CTO博客作者wespten的原创作品，请联系作者获取转载授权，否则将追究法律责任
深入学习java源码之CharSequence.chars()CharSequence.codePoints()
String 是java中的字符串，它继承于CharSequence。
String类所包含的API接口非常多。为了便于今后的使用，我对String的API进行了分类，并都给出的演示程序。
String 和 CharSequence 关系
String 继承于CharSequence，也就是说String也是CharSequence类型。
CharSequence是一个接口，它只包括length(), charAt(int index), subSequence(int start, int end)这几个API接口。除了String实现了CharSequence之外，StringBuffer和StringBuilder也实现了CharSequence接口。
需要说明的是，CharSequence就是字符序列，String, StringBuilder和StringBuffer本质上都是通过字符数组实现的！
StringBuilder 和 StringBuffer 的区别
StringBuilder 和 StringBuffer都是可变的字符序列。它们都继承于AbstractStringBuilder，实现了CharSequence接口。
但是，StringBuilder是非线程安全的，而StringBuffer是线程安全的。
charSequence是一个接口，表示char值的一个可读序列。此接口对许多不同种类的char序列提供统一的自读访问。此接口不修改该equals和hashCode方法的常规协定，因此，通常未定义比较实现 CharSequence 的两个对象的结果。他有几个实现类：CharBuffer、String、StringBuffer、StringBuilder。
java8新增2个default方法
public default IntStream chars()
public default IntStream codePoints()
分别转换为以char和codepoint为单位的java stream.注意转换后为int类型的unicode编码.
函数式接口Consumer
package jdk8;
import java.util.function.Consumer;
public class ConsumerTest {
public static void main(String[] args) {
testConsumer();
testAndThen();
}
/**
* 一个简单的平方计算
*/
public static void testConsumer(){
Consumer<Integer> square = x -> System.out.println("print square : " + x * x);
square.accept(2);
}
/**
* 定义3个Consumer并按顺序进行调用andThen方法，其中consumer2抛出NullPointerException。
*/
public static void testAndThen(){
Consumer<Integer> consumer1 = x -> System.out.println("first x : " + x);
Consumer<Integer> consumer2 = x -> {
System.out.println("second x : " + x);
throw new NullPointerException("throw exception test");
};
Consumer<Integer> consumer3 = x -> System.out.println("third x : " + x);
consumer1.andThen(consumer2).andThen(consumer3).accept(1);
}
}
下面是执行结果：
print square : 4
first x : 1
second x : 1
Exception in thread "main" java.lang.NullPointerException: throw exception test
at jdk8.ConsumerTest.lambda$testAndThen$2(ConsumerTest.java:27)
at java.util.function.Consumer.lambda$andThen$0(Consumer.java:65)
at java.util.function.Consumer.lambda$andThen$0(Consumer.java:65)
at jdk8.ConsumerTest.testAndThen(ConsumerTest.java:31)
at jdk8.ConsumerTest.main(ConsumerTest.java:9)
Process finished with exit code 1
在testAndThen()方法的执行结果可以看到打印的顺序和出现异常的情况（third x : 1 并没有输出）
foreach
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}Consumer的accept只接受一个参数，那如果要是想使用多个参数要怎么办？jdk8又提供了一个BiConsumer接口类，该类与Consumer的区别是可以接受2个参数。
java源码
Modifier and Type
| Method and Description
|
char | charAt(int index) 返回 char指定索引处的值。 |
default IntStream | chars() 返回一个 int的流，从这个序列中零扩展 char值。 |
default IntStream | codePoints() 从此序列返回码流值。 |
int | length() 返回此字符序列的长度。 |
CharSequence | subSequence(int start, int end) 返回一个 CharSequence ，这是这个序列的一个子序列。 |
String | toString() 以与此顺序相同的顺序返回包含此序列中的字符的字符串。 |
package java.lang;
import java.util.NoSuchElementException;
import java.util.PrimitiveIterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.IntConsumer;
import java.util.stream.IntStream;
import java.util.stream.StreamSupport;
public interface CharSequence {
int length();
char charAt(int index);
CharSequence subSequence(int start, int end);
public String toString();
public default IntStream chars() {
class CharIterator implements PrimitiveIterator.OfInt {
int cur = 0;
public boolean hasNext() {
return cur < length();
}
public int nextInt() {
if (hasNext()) {
return charAt(cur++);
} else {
throw new NoSuchElementException();
}
}
@Override
public void forEachRemaining(IntConsumer block) {
for (; cur < length(); cur++) {
block.accept(charAt(cur));
}
}
}
return StreamSupport.intStream(() ->
Spliterators.spliterator(
new CharIterator(),
length(),
Spliterator.ORDERED),
Spliterator.SUBSIZED | Spliterator.SIZED | Spliterator.ORDERED,
false);
}
public default IntStream codePoints() {
class CodePointIterator implements PrimitiveIterator.OfInt {
int cur = 0;
@Override
public void forEachRemaining(IntConsumer block) {
final int length = length();
int i = cur;
try {
while (i < length) {
char c1 = charAt(i++);
if (!Character.isHighSurrogate(c1) || i >= length) {
block.accept(c1);
} else {
char c2 = charAt(i);
if (Character.isLowSurrogate(c2)) {
i++;
block.accept(Character.toCodePoint(c1, c2));
} else {
block.accept(c1);
}
}
}
} finally {
cur = i;
}
}
public boolean hasNext() {
return cur < length();
}
public int nextInt() {
final int length = length();
if (cur >= length) {
throw new NoSuchElementException();
}
char c1 = charAt(cur++);
if (Character.isHighSurrogate(c1) && cur < length) {
char c2 = charAt(cur);
if (Character.isLowSurrogate(c2)) {
cur++;
return Character.toCodePoint(c1, c2);
}
}
return c1;
}
}
return StreamSupport.intStream(() ->
Spliterators.spliteratorUnknownSize(
new CodePointIterator(),
Spliterator.ORDERED),
Spliterator.ORDERED,
false);
}
}
Modifier and Type
| Method and Description
|
void | forEachRemaining(T_CONS 对每个剩余的元素执行给定的动作，按照迭代时发生的顺序，直到所有元素都被处理或动作引发异常。 |
package java.util;
import java.util.function.Consumer;
import java.util.function.DoubleConsumer;
import java.util.function.IntConsumer;
import java.util.function.LongConsumer;
public interface PrimitiveIterator<T, T_CONS> extends Iterator<T> {
@SuppressWarnings("overloads")
void forEachRemaining(T_CONS action);
/**
* An Iterator specialized for {@code int} values.
* @since 1.8
*/
public static interface OfInt extends PrimitiveIterator<Integer, IntConsumer> {
int nextInt();
default void forEachRemaining(IntConsumer action) {
Objects.requireNonNull(action);
while (hasNext())
action.accept(nextInt());
}
@Override
default Integer next() {
if (Tripwire.ENABLED)
Tripwire.trip(getClass(), "{0} calling PrimitiveIterator.OfInt.nextInt()");
return nextInt();
}
@Override
default void forEachRemaining(Consumer<? super Integer> action) {
if (action instanceof IntConsumer) {
forEachRemaining((IntConsumer) action);
}
else {
// The method reference action::accept is never null
Objects.requireNonNull(action);
if (Tripwire.ENABLED)
Tripwire.trip(getClass(), "{0} calling PrimitiveIterator.OfInt.forEachRemainingInt(action::accept)");
forEachRemaining((IntConsumer) action::accept);
}
}
}
public static interface OfLong extends PrimitiveIterator<Long, LongConsumer> {
long nextLong();
default void forEachRemaining(LongConsumer action) {
Objects.requireNonNull(action);
while (hasNext())
action.accept(nextLong());
}
@Override
default Long next() {
if (Tripwire.ENABLED)
Tripwire.trip(getClass(), "{0} calling PrimitiveIterator.OfLong.nextLong()");
return nextLong();
}
@Override
default void forEachRemaining(Consumer<? super Long> action) {
if (action instanceof LongConsumer) {
forEachRemaining((LongConsumer) action);
}
else {
// The method reference action::accept is never null
Objects.requireNonNull(action);
if (Tripwire.ENABLED)
Tripwire.trip(getClass(), "{0} calling PrimitiveIterator.OfLong.forEachRemainingLong(action::accept)");
forEachRemaining((LongConsumer) action::accept);
}
}
}
public static interface OfDouble extends PrimitiveIterator<Double, DoubleConsumer> {
double nextDouble();
default void forEachRemaining(DoubleConsumer action) {
Objects.requireNonNull(action);
while (hasNext())
action.accept(nextDouble());
}
@Override
default Double next() {
if (Tripwire.ENABLED)
Tripwire.trip(getClass(), "{0} calling PrimitiveIterator.OfDouble.nextLong()");
return nextDouble();
}
@Override
default void forEachRemaining(Consumer<? super Double> action) {
if (action instanceof DoubleConsumer) {
forEachRemaining((DoubleConsumer) action);
}
else {
// The method reference action::accept is never null
Objects.requireNonNull(action);
if (Tripwire.ENABLED)
Tripwire.trip(getClass(), "{0} calling PrimitiveIterator.OfDouble.forEachRemainingDouble(action::accept)");
forEachRemaining((DoubleConsumer) action::accept);
}
}
}
}
函数式接口
package java.util.function;
import java.util.Objects;
@FunctionalInterface
public interface Consumer<T> {
void accept(T t);
default Consumer<T> andThen(Consumer<? super T> after) {
Objects.requireNonNull(after);
return (T t) -> { accept(t); after.accept(t); };
}
}
package java.util.function;
import java.util.Objects;
@FunctionalInterface
public interface DoubleConsumer {
void accept(double value);
default DoubleConsumer andThen(DoubleConsumer after) {
Objects.requireNonNull(after);
return (double t) -> { accept(t); after.accept(t); };
}
}
package java.util.function;
import java.util.Objects;
@FunctionalInterface
public interface IntConsumer {
void accept(int value);
default IntConsumer andThen(IntConsumer after) {
Objects.requireNonNull(after);
return (int t) -> { accept(t); after.accept(t); };
}
}
package java.util.function;
import java.util.Objects;
@FunctionalInterface
public interface LongConsumer {
void accept(long value);
default LongConsumer andThen(LongConsumer after) {
Objects.requireNonNull(after);
return (long t) -> { accept(t); after.accept(t); };
}
}
package java.util;
import java.util.function.Consumer;
public interface Iterator<E> {
boolean hasNext();
E next();
default void remove() {
throw new UnsupportedOperationException("remove");
}
default void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
while (hasNext())
action.accept(next());
}
}
