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。