Flips测试类（page43）

public class Flips {
    
    public static void main(String[] args) {
        
        int T = Integer.parseInt(args[0]);
        Counter heads = new Counter("heads");
        Counter tails = new Counter("tails");
        
        for (int t = 0; t < T; t++) 
            if(StdRandom.bernoulli(0.5))
                heads.increment();
            else tails.increment();
        StdOut.println(heads);
        StdOut.println(tails);
        int d = heads.tally() - tails.tally();
        StdOut.println("delta : " + Math.abs(d));
    }
}

打印结果：public class Counter implements Comparable<Counter> {

    private final String name;     // counter name
    private int count = 0;         // current value

    /**
     * Initializes a new counter starting at 0, with the given id.
     * @param id the name of the counter
     */
    public Counter(String id) {
        name = id;
    } 

    /**
     * Increments the counter by 1.
     */
    public void increment() {
        count++;
    } 

    /**
     * Returns the current count.
     */
    public int tally() {
        return count;
    } 

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

    /**
     * Compares this counter to that counter.
     */
    public int compareTo(Counter that) {
        if      (this.count < that.count) return -1;
        else if (this.count > that.count) return +1;
        else                              return  0;
    }
} 

public class Flips {
    
    public static void main(String[] args) {
        
        Counter c1 = new Counter("ones");
        c1.increment();
        Counter c2 = c1;
        c2.increment();
        StdOut.println(c1);
    }
}
//赋值语句的区别： 复制的是引用类型还是原始数据类型。