我需要在Java中连接两个字符串数组。
void f(String[] first, String[] second) {
String[] both = ???
}
哪种方法最简单?
我需要在Java中连接两个字符串数组。
void f(String[] first, String[] second) {
String[] both = ???
}
哪种方法最简单?
当前回答
这里是silvertab编写的伪代码解决方案的工作代码中的一个可能实现。
谢谢silvertab!
public class Array {
public static <T> T[] concat(T[] a, T[] b, ArrayBuilderI<T> builder) {
T[] c = builder.build(a.length + b.length);
System.arraycopy(a, 0, c, 0, a.length);
System.arraycopy(b, 0, c, a.length, b.length);
return c;
}
}
接下来是构建器界面。
注意:构建器是必要的,因为在java中不可能这样做
新T[尺寸]
由于通用类型擦除:
public interface ArrayBuilderI<T> {
public T[] build(int size);
}
这里是一个实现接口的具体构建器,构建一个整数数组:
public class IntegerArrayBuilder implements ArrayBuilderI<Integer> {
@Override
public Integer[] build(int size) {
return new Integer[size];
}
}
最后是应用程序/测试:
@Test
public class ArrayTest {
public void array_concatenation() {
Integer a[] = new Integer[]{0,1};
Integer b[] = new Integer[]{2,3};
Integer c[] = Array.concat(a, b, new IntegerArrayBuilder());
assertEquals(4, c.length);
assertEquals(0, (int)c[0]);
assertEquals(1, (int)c[1]);
assertEquals(2, (int)c[2]);
assertEquals(3, (int)c[3]);
}
}
其他回答
我测试了以下代码,工作正常
我还使用了library:org.apache.mons.lang.ArrayUtils
public void testConcatArrayString(){
String[] a = null;
String[] b = null;
String[] c = null;
a = new String[] {"1","2","3","4","5"};
b = new String[] {"A","B","C","D","E"};
c = (String[]) ArrayUtils.addAll(a, b);
if(c!=null){
for(int i=0; i<c.length; i++){
System.out.println("c[" + (i+1) + "] = " + c[i]);
}
}
}
当做
哇!这里有很多复杂的答案,包括一些依赖于外部依赖的简单答案。这样做怎么样:
String [] arg1 = new String{"a","b","c"};
String [] arg2 = new String{"x","y","z"};
ArrayList<String> temp = new ArrayList<String>();
temp.addAll(Arrays.asList(arg1));
temp.addAll(Arrays.asList(arg2));
String [] concatedArgs = temp.toArray(new String[arg1.length+arg2.length]);
这可能是唯一通用且类型安全的方法:
public class ArrayConcatenator<T> {
private final IntFunction<T[]> generator;
private ArrayConcatenator(IntFunction<T[]> generator) {
this.generator = generator;
}
public static <T> ArrayConcatenator<T> concat(IntFunction<T[]> generator) {
return new ArrayConcatenator<>(generator);
}
public T[] apply(T[] array1, T[] array2) {
T[] array = generator.apply(array1.length + array2.length);
System.arraycopy(array1, 0, array, 0, array1.length);
System.arraycopy(array2, 0, array, array1.length, array2.length);
return array;
}
}
用法非常简洁:
Integer[] array1 = { 1, 2, 3 };
Double[] array2 = { 4.0, 5.0, 6.0 };
Number[] array = concat(Number[]::new).apply(array1, array2);
(需要静态导入)
拒绝无效的数组类型:
concat(String[]::new).apply(array1, array2); // error
concat(Integer[]::new).apply(array1, array2); // error
使用Java集合
好吧,Java没有提供连接数组的助手方法。然而,自Java5以来,Collections实用程序类引入了addAll(Collection<?super T>c,T…elements)方法。
我们可以创建一个List对象,然后调用该方法两次,将这两个数组添加到列表中。最后,我们将生成的List转换回数组:
static <T> T[] concatWithCollection(T[] array1, T[] array2) {
List<T> resultList = new ArrayList<>(array1.length + array2.length);
Collections.addAll(resultList, array1);
Collections.addAll(resultList, array2);
@SuppressWarnings("unchecked")
//the type cast is safe as the array1 has the type T[]
T[] resultArray = (T[]) Array.newInstance(array1.getClass().getComponentType(), 0);
return resultList.toArray(resultArray);
}
Test
@Test
public void givenTwoStringArrays_whenConcatWithList_thenGetExpectedResult() {
String[] result = ArrayConcatUtil.concatWithCollection(strArray1, strArray2);
assertThat(result).isEqualTo(expectedStringArray);
}
算法爱好者的另一个答案是:
public static String[] mergeArrays(String[] array1, String[] array2) {
int totalSize = array1.length + array2.length; // Get total size
String[] merged = new String[totalSize]; // Create new array
// Loop over the total size
for (int i = 0; i < totalSize; i++) {
if (i < array1.length) // If the current position is less than the length of the first array, take value from first array
merged[i] = array1[i]; // Position in first array is the current position
else // If current position is equal or greater than the first array, take value from second array.
merged[i] = array2[i - array1.length]; // Position in second array is current position minus length of first array.
}
return merged;
用法:
String[] array1str = new String[]{"a", "b", "c", "d"};
String[] array2str = new String[]{"e", "f", "g", "h", "i"};
String[] listTotalstr = mergeArrays(array1str, array2str);
System.out.println(Arrays.toString(listTotalstr));
结果:
[a, b, c, d, e, f, g, h, i]