Question

Counter c1 = new Counter("ones"); 
c1.increment(); 
Counter c2 = c1; 
c2.increment(); 
StdOut.println(c1);

类代码链接：https://introcs.cs.princeton.edu/java/33design/Counter.java

public class Counter implements Comparable<Counter> {

    private final String name;     // counter name
    private final int maxCount;    // maximum value
    private int count;             // current value

    // create a new counter with the given parameters
    public Counter(String id, int max) {
        name = id;
        maxCount = max;
        count = 0;
    } 

    // increment the counter by 1
    public void increment() {
         if (count < maxCount) count++;
    } 

    // return the current count
    public int value() {
        return count;
    } 

    // return a string representation of this counter
    public String toString() {
        return name + ": " + count;
    } 

    // compare two Counter objects based on their count
    public int compareTo(Counter that) {
        if      (this.count < that.count) return -1;
        else if (this.count > that.count) return +1;
        else                              return  0;
    }


    // test client
    public static void main(String[] args) { 
        int n = Integer.parseInt(args[0]);
        int trials = Integer.parseInt(args[1]);

        // create n counters
        Counter[] hits = new Counter[n];
        for (int i = 0; i < n; i++) {
            hits[i] = new Counter(i + "", trials);
        }

        // increment trials counters at random
        for (int t = 0; t < trials; t++) {
            int index = StdRandom.uniform(n);
            hits[index].increment();
        }

        // print results
        for (int i = 0; i < n; i++) {
            StdOut.println(hits[i]);
        }
    } 
}

这本书说它将打印“ 2ones”，过程如上图所示。但是我不明白。在我看来，c1加，所以它的对象也加，所以我们得到“ 2”；然后将c1复制到c2，c2也得到“ 2”。随着c2的添加，对象将转向未知的下一个网格。当打印c1时，我认为我们应该得到“ 2”而不是“ 2ones”。那我的程序怎么了？预先感谢。

Answer 1

Counter c1 = new Counter("ones"); 
c1.increment(); 
Counter c2 = c1; 
c2.increment(); 
StdOut.println(c1);

我认为此演示应仅显示引用。由于您仅创建1个类型为counter的对象。然后将c1的值分配给变量（Counter）c2，然后对变量c2使用.increment（）方法，则c1将更改。由于c2和c1都引用内存中的同一对象。因此，更改c1和c2都会影响同一对象。

算法，第4版：不了解有关别名/引用的示例

1 个答案: