从实现toString：
public String toString() { StringBuilder result = new StringBuilder(); String newline = System.getProperty("line.separator"); result.append( this.getClass().getName() ); result.append( " Object {" ); result.append(newline); //determine fields declared in this class only (no fields of superclass) Field[] fields = this.getClass().getDeclaredFields(); //print field names paired with their values for ( Field field : fields ) { result.append(" "); try { result.append( field.getName() ); result.append(": "); //requires access to private field: result.append( field.get(this) ); } catch ( IllegalAccessException ex ) { System.out.println(ex); } result.append(newline); } result.append("}"); return result.toString();}
