ArrayList<ArrayList<Object>> a = new ArrayList<>();  // 打造这样一个数据的集合 [[1,2],[2,3]] 要求 生成字符串 [1,2]#[2,3]
    for (int i = 0; i < 2; i++) { 
      ArrayList<Object> c = new ArrayList<>();
      c.add(i+1);
      c.add(i+2);
      a.add(c);
      //打印单个子集合的字符串形式数据
      Log.i("myinfo",c.toString());
    }
    StringBuilder builder = new StringBuilder();
    builder.append(a.get(0).toString()+"#"+a.get(1).toString());
    //打印该集合的字符串形式数据
    Log.i("myinfo",builder.toString());

 /**
   * Returns the string representation of this {@code Collection}. The presentation
   * has a specific format. It is enclosed by square brackets ("[]"). Elements
   * are separated by ', ' (comma and space).
   *
   * @return the string representation of this {@code Collection}.
   */
  @Override
  public String toString() {
    if (isEmpty()) {
      return "[]";
    }
    StringBuilder buffer = new StringBuilder(size() * 16);
    buffer.append('[');
    Iterator<?> it = iterator();
    while (it.hasNext()) {
      Object next = it.next();
      if (next != this) {
        buffer.append(next);
      } else {
        buffer.append("(this Collection)");
      }
      if (it.hasNext()) {
        buffer.append(", ");
      }
    }
    buffer.append(']');
    return buffer.toString();
  }

   if (next != this) {
        buffer.append(next);
      } else {
        buffer.append("(this Collection)");
      }

ArrayList<ArrayList<Object>> a = new ArrayList<>();
    for (int i = 0; i < 2; i++) {
      ArrayList<Object> c = new ArrayList<>();
      c.add(i+1);
      c.add(i+2);
      c.add(c);
      //打印单个子集合的字符串形式数据
      Log.i("myinfo",c.toString());
    }

/**
   * Returns a string containing a concise, human-readable description of this
   * object. Subclasses are encouraged to override this method and provide an
   * implementation that takes into account the object's type and data. The
   * default implementation is equivalent to the following expression:
   * <pre>
   *  getClass().getName() + '@' + Integer.toHexString(hashCode())</pre>
   * <p>See <a href="{@docRoot}reference/java/lang/Object.html#writing_toString">Writing a useful
   * {@code toString} method</a>
   * if you intend implementing your own {@code toString} method.
   *
   * @return a printable representation of this object.
   */
  public String toString() {
    return getClass().getName() + '@' + Integer.toHexString(hashCode());
  }

getClass().getName() + '@' + Integer.toHexString(hashCode())</pre>

getClass().getName()返回对象所属类的类名
hashCode()返回该对象的哈希值
Integer.toHexString(hashCode())将对象的哈希值用16进制表示

Object d = new Object();
Log.i("myinfo",d.toString());

  /**
   * Returns this string.
   */
  @Override
  public String toString() {
    return this;
  }

/**
   * Returns the contents of this builder.
   *
   * @return the string representation of the data in this builder.
   */
  @Override
  public String toString() {
    /* Note: This method is required to workaround a compiler bug
     * in the RI javac (at least in 1.5.0_06) that will generate a
     * reference to the non-public AbstractStringBuilder if we don't
     * override it here.
     */
    return super.toString();
  }

 /**
   * Returns the current String representation.
   *
   * @return a String containing the characters in this instance.
   */
  @Override
  public String toString() {
    if (count == 0) {
      return "";
    }
    return StringFactory.newStringFromChars(0, count, value);
  }

@Override
  public synchronized String toString() {
    return super.toString();
  }

/**
   * Returns the current String representation.
   *
   * @return a String containing the characters in this instance.
   */
  @Override
  public String toString() {
    if (count == 0) {
      return "";
    }
    return StringFactory.newStringFromChars(0, count, value);
  }

public String toString() {
    Iterator<Entry<K,V>> i = entrySet().iterator();
    if (! i.hasNext())
      return "{}";
    StringBuilder sb = new StringBuilder();
    sb.append('{');
    for (;;) {
      Entry<K,V> e = i.next();
      K key = e.getKey();
      V value = e.getValue();
      sb.append(key  == this ? "(this Map)" : key);
      sb.append('=');
      sb.append(value == this ? "(this Map)" : value);
      if (! i.hasNext())
        return sb.append('}').toString();
      sb.append(',').append(' ');
    }
  }

 Map<String,String> map = new HashMap<>();
    map.put("keyA","valueA");
    map.put("keyB","valueB");
    map.put("keyC","valueC");
    Log.i("myinfo",map.toString());

05-12 11:41:30.898 4490-4490/com.maiji.magkarepatient I/myinfo: {keyA=valueA, keyB=valueB, keyC=valueC}