Java增强for循环中获取index

最新推荐文章于 2024-08-17 03:40:45 发布

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本文介绍Java中几种不同的循环方法，包括普通for循环、增强for循环、自定义静态方法实现的带索引循环、扩展Iterable实现的带索引循环及jQuery风格的循环。每种方法都附有示例代码。

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[b]前提测试数据：[/b]


String[] data = new String[]{"rensanning001", "rensanning002", "rensanning003"};
List<String> dataList = Arrays.asList(data);

[b]普通的For循环：[/b]


for (int i = 0; i < dataList.size(); i++) {
  System.out.println(i + ":" + dataList.get(i));
}

[b]增强For循环（获取index需要定义额外的变量）：[/b]


int i = 0;
for (String elem : dataList) {
  System.out.println(i + ":" + elem);
  i++;
}

[b]自定义静态方法实现带index的循环：[/b]


for (Indexer<String> elem : ExtFor1.loop(dataList)) {
  System.out.println(elem.index() + ":" + elem.value());
}


public class ExtFor1 {

	public static <T> Iterable<Indexer<T>> loop(final Iterable<T> list) {
		return new Iterable<Indexer<T>>() {
			@Override
			public Iterator<Indexer<T>> iterator() {
				return new Iterator<Indexer<T>>() {
					private int counter = 0;
					private Iterator<T> iterator = list.iterator();

					@Override
					public boolean hasNext() {
						return iterator.hasNext();
					}

					@Override
					public Indexer<T> next() {
						Indexer<T> elem = new Indexer<T>(counter++, iterator.next());
						return elem;
					}

					@Override
					public void remove() {
						throw new RuntimeException();
					}
				};
			}
		};
	}

}

[b]扩展Iterable实现带index的循环：[/b]


for (Indexer<String> elem : ExtFor2.loop(dataList)) {
  System.out.println(elem.index() + ":" + elem.value());
}


public class ExtFor2<T> implements Iterable<Indexer<T>> {
    private Iterator<T> iterator;

    private ExtFor2(Iterable<T> iter) {
        this.iterator = iter.iterator();
    }

    public static <T> ExtFor2<T> loop(Iterable<T> iter) {
        return new ExtFor2<T>(iter);
    }

    @Override
    public Iterator<Indexer<T>> iterator() {
		return new Iterator<Indexer<T>>() {
			private int counter = 0;

			@Override
			public boolean hasNext() {
				return iterator.hasNext();
			}

			@Override
			public Indexer<T> next() {
				Indexer<T> elem = new Indexer<T>(counter++, iterator.next());
				return elem;
			}

			@Override
			public void remove() {
				throw new RuntimeException();
			}
		};
	}

}

[b]jquery风格的for循环：[/b]


For.each(dataList, new For.Function<String>() {
  public void execute(int index, String elem) {
    System.out.println(index + ":" + elem);
  }
});


public class For {

	public static <T> void each(List<T> list, Function<T> function) {
		int length = list.size();
		for (int index = 0; index < length; index++) {
			function.execute(index, list.get(index)); 
		}
	}

	public static interface Function<T> {
		public void execute(int index, T obj);
	}
}


public class Indexer<T> {
	private final int index;
	private final T value;

	public Indexer(int index, T value) {
		this.index = index;
		this.value = value;
	}

	public int index() {
		return this.index;
	}

	public T value() {
		return this.value;
	}
}