小编典典

.clone()或Arrays.copyOf()?

java

为了减少可变性,我们应该使用

public void setValues(String[] newVals) {

     this.vals = ( newVals == null ? null : newVals.clone() );
}

要么

public void setValues(String[] newVals) {

     this.vals = ( newVals == null ? null : Arrays.copyOf(newVals, newVals.length) );
}

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2020-09-08

共1个答案

小编典典

使用jmh更新

使用jmh,我得到类似的结果,除了clone似乎稍微好一点。

原始帖子

我对性能进行了一个快速测试:cloneSystem.arrayCopy并且Arrays.copyOf具有非常相似的性能(jdk
1.7.06,服务器虚拟机)。

有关详细信息(以毫秒为单位),请在JIT之后:

克隆:68个
数组复制:68个
Arrays.copyOf:68

测试代码:

public static void main(String[] args) throws InterruptedException,
        IOException {
    int sum = 0;
    int[] warmup = new int[1];
    warmup[0] = 1;
    for (int i = 0; i < 15000; i++) { // triggers JIT
        sum += copyClone(warmup);
        sum += copyArrayCopy(warmup);
        sum += copyCopyOf(warmup);
    }

    int count = 10_000_000;
    int[] array = new int[count];
    for (int i = 0; i < count; i++) {
        array[i] = i;
    }

    // additional warmup for main
    for (int i = 0; i < 10; i++) {
        sum += copyArrayCopy(array);
    }
    System.gc();
    // copyClone
    long start = System.nanoTime();
    for (int i = 0; i < 10; i++) {
        sum += copyClone(array);
    }
    long end = System.nanoTime();
    System.out.println("clone: " + (end - start) / 1000000);
    System.gc();
    // copyArrayCopy
    start = System.nanoTime();
    for (int i = 0; i < 10; i++) {
        sum += copyArrayCopy(array);
    }
    end = System.nanoTime();
    System.out.println("arrayCopy: " + (end - start) / 1000000);
    System.gc();
    // copyCopyOf
    start = System.nanoTime();
    for (int i = 0; i < 10; i++) {
        sum += copyCopyOf(array);
    }
    end = System.nanoTime();
    System.out.println("Arrays.copyOf: " + (end - start) / 1000000);
    // sum
    System.out.println(sum);
}

private static int copyClone(int[] array) {
    int[] copy = array.clone();
    return copy[copy.length - 1];
}

private static int copyArrayCopy(int[] array) {
    int[] copy = new int[array.length];
    System.arraycopy(array, 0, copy, 0, array.length);
    return copy[copy.length - 1];
}

private static int copyCopyOf(int[] array) {
    int[] copy = Arrays.copyOf(array, array.length);
    return copy[copy.length - 1];
}
2020-09-08