java基础---->数组的基础使用（一）

　　数组是一种效率最高的存储和随机访问对象引用序列的方式，我们今天来对数组做简单的介绍。手写瑶笺被雨淋，模糊点画费探寻，纵然灭却书中字，难灭情人一片心。

数组的简单使用

一、数组的赋值

String[] arrays = new String[]{"linux", "huhx", "android"};
//arrays[4] = "tomhu"; // 数组越界
String[] arrays2 = arrays;
arrays2[1] = "chenhui"; // 修改arrays2的值，对arrays产生了影响
System.out.println(Arrays.toString(arrays)); // [linux, chenhui, android]
arrays[2] = "google";
System.out.println(Arrays.toString(arrays2)); // [linux, chenhui, google]

二、数组的深复制

String[] arrays3 = Arrays.copyOf(arrays, arrays.length); // 底部实现仍然是System.arrarycopy()方法
System.out.println(Arrays.toString(arrays3)); // [linux, chenhui, google]
arrays3[1] = "nodeJS"; // 修改arrays3的值，对arrays没有影响
System.out.println(Arrays.toString(arrays)); // [linux, chenhui, google]

三、数组的填充

String[] arrays4 = new String[4];
Arrays.fill(arrays4, "linux");
System.out.println(Arrays.toString(arrays4)); // [linux, linux, linux, linux]

四、数组内容的比较

boolean arraysEqual = Arrays.equals(arrays3, arrays);
System.out.println(arraysEqual); // false
System.out.println(Arrays.equals(arrays, arrays2)); // true

五、数组的排序，改变了数组本身

Arrays.sort(arrays);
System.out.println(Arrays.toString(arrays)); // [chenhui, google, linux]

六、数组内元素的查找

int location = Arrays.binarySearch(arrays, "linux");
System.out.println(location); // 2

七、数组生成ArrayList

List<String> strings = Arrays.asList(arrays);
Iterator<String> iterator = strings.iterator();
while (iterator.hasNext()) {
    System.out.print(iterator.next());
}

对Arrays类方法的分析

一、fill填充方法

public static void fill(Object[] a, Object val) {
    for (int i = 0, len = a.length; i < len; i++)
        a[i] = val;
}

二、toString打印方法

public static String toString(Object[] a) {
    if (a == null)
        return "null";

    int iMax = a.length - 1;
    if (iMax == -1)
        return "[]";

    StringBuilder b = new StringBuilder();
    b.append('[');
    for (int i = 0; ; i++) {
        b.append(String.valueOf(a[i]));
        if (i == iMax)
            return b.append(']').toString();
        b.append(", ");
    }
}

三、equal比较方法

public static boolean equals(Object[] a, Object[] a2) {
    if (a==a2)
        return true;
    if (a==null || a2==null)
        return false;

    int length = a.length;
    if (a2.length != length)
        return false;

    for (int i=0; i<length; i++) {
        Object o1 = a[i];
        Object o2 = a2[i];
        if (!(o1==null ? o2==null : o1.equals(o2)))
            return false;
    }

    return true;
}

四、asList转换成列表的方法

@SafeVarargs
public static <T> List<T> asList(T... a) {
    return new ArrayList<>(a);
}

五、iterator遍历方法

public Iterator<E> iterator() {
    return new Itr();
}

/**
 * An optimized version of AbstractList.Itr
 */
private class Itr implements Iterator<E> {
    int cursor;       // index of next element to return
    int lastRet = -1; // index of last element returned; -1 if no such
    int expectedModCount = modCount;

    public boolean hasNext() {
        return cursor != size;
    }

    @SuppressWarnings("unchecked")
    public E next() {
        checkForComodification(); // 检查数组内容的一致性
        int i = cursor;
        if (i >= size)
            throw new NoSuchElementException();
        Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length)
            throw new ConcurrentModificationException();
        cursor = i + 1;
        return (E) elementData[lastRet = i];
    }

    public void remove() {
        if (lastRet < 0)
            throw new IllegalStateException();
        checkForComodification();

        try {
            ArrayList.this.remove(lastRet);
            cursor = lastRet;
            lastRet = -1;
            expectedModCount = modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }

    final void checkForComodification() {
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}

友情链接