JDK之java.util.Arrays-白红宇

JDK之java.util.Arrays

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发布时间：2019-05-26

本文共 2962 字，大约阅读时间需要 9 分钟。

功能

JDK1.2起提供的工具类，实现对数组的排序、查找、复制等操作

源码

Sorting methods

public static void sort(int[] a) {
       DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);}public static void sort(int[] a, int fromIndex, int toIndex) {
       rangeCheck(a.length, fromIndex, toIndex);    DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);}

Swaps x[a] with x[b]

private static void swap(Object[] x, int a, int b) {
       Object t = x[a];    x[a] = x[b];    x[b] = t;}

Searching

public static int binarySearch(long[] a, long key) {
       return binarySearch0(a, 0, a.length, key);}public static int binarySearch(long[] a, int fromIndex, int toIndex,                               long key) {
       rangeCheck(a.length, fromIndex, toIndex);    return binarySearch0(a, fromIndex, toIndex, key);}

Equality Testing

public static boolean equals(long[] a, long[] 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

Filling

public static void fill(long[] a, long val) {
       // 定义变量len，执行效率高点    for (int i = 0, len = a.length; i < len; i++)        a[i] = val;} public static void fill(long[] a, int fromIndex, int toIndex, long val) {
       rangeCheck(a.length, fromIndex, toIndex);    for (int i = fromIndex; i < toIndex; i++)        a[i] = val;}

toString

public static String toString(long[] 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(a[i]);        if (i == iMax)            return b.append(']').toString();        b.append(", ");    }}

asList

// JAVA5 可变参数 @SafeVarargs @SuppressWarnings("varargs") public static 
   
     List
    
      asList(T... a) {
        return new ArrayList<>(a); }

注意，asList返回的list不支持添加操作

public static void main(String[] args) {
       // 类型类：java.util.Arrays$ArrayList    List stooges = Arrays.asList("Larry", "Moe", "Curly");    // 不可添加元素 java.lang.UnsupportedOperationException    // stooges.add("ee");    // 类型类：java.util.ArrayList    ArrayList
   
     list = new ArrayList<>(stooges);    list.add("diligent");    // JDK5增强for循环    for(String t : list){
           System.out.println(t);    }    System.out.println(list.size());}

Cloning

@SuppressWarnings("unchecked")public static 
   
     T[] copyOf(T[] original, int newLength) {
       return (T[]) copyOf(original, newLength, original.getClass());}public static 
    
      T[] copyOf(U[] original, int newLength, Class
      newType) {
       @SuppressWarnings("unchecked")    T[] copy = ((Object)newType == (Object)Object[].class)        ? (T[]) new Object[newLength]        : (T[]) Array.newInstance(newType.getComponentType(), newLength);    System.arraycopy(original, 0, copy, 0,                     Math.min(original.length, newLength));    return copy;}

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