计算器不能执行计算功能，运算结果始终为0

Question

部分代码：public void onClick(View v) { // TODO Auto-generated method stub           String str=t1.getText().toString(); switch(v.getId()){ case R.id.button16: case R.id.button13: case R.id.button14: case R.id.button15: case R.id.button9: case R.id.button10: case R.id.button11: case R.id.button5: case R.id.button6: case R.id.button7: case R.id.button17: if(clear_flag){ clear_flag=false; str=""; t1.setText(""); }  t1.setText(str+((Button)v).getText());   break; case R.id.button12: case R.id.button8: case R.id.button4: case R.id.button3: if(clear_flag){ clear_flag=false; str=""; t1.setText(""); } t1.setText(str+" "+((Button)v).getText()+" "); break; case R.id.button2: if(clear_flag){ clear_flag=false; str=""; t1.setText(""); } else if(str!=null&&!str.equals("")){ t1.setText(str.substring(0,str.length()-1)); }    break; case R.id.button1: clear_flag=false; str="";    t1.setText(" "); break; case R.id.button18: getResult(); break;  } }private void getResult(){ String exp=t1.getText().toString(); if(exp==null||exp.equals(" ")){ return; } if(!exp.contains(" ")){ return; } if(clear_flag){ clear_flag=false; return; } clear_flag=true; double result=0; String s1=exp.substring(0,exp.indexOf("")); String op=exp.substring(exp.indexOf("")+1,exp.indexOf("")+2); String s2=exp.substring(exp.indexOf("")+3); if(!s1.equals("")&&!s2.equals("")){ double d1=Double.parseDouble(s1); double d2=Double.parseDouble(s2); if(op.equals("+")){ result=d1+d2; }else if(op.equals("-")){ result=d1-d2; }else if(op.equals("*")){ result=d1*d2; }else if(op.equals("/")){ if(d2==0){ result=0;}else{ result=d1/d2; }    } if(!s1.contains(".")&&!s2.contains(".")&&!op.equals('/')){ int r=(int)result; t1.setText(r+""); }else{ t1.setText(result+"");} }else if(!s1.equals("")&&s2.equals("")){ t1.setText(exp); }else if(s1.equals("")&&!s2.equals("")){ double d2=Double.parseDouble(s2); if(op.equals("+")){ result=0+d2; }else if(op.equals("-")){ result=0-d2; }else if(op.equals("*")){ result=0; }else if(op.equals("/")){ result=0; } if(!s2.contains(".")){ int r=(int)result; t1.setText(r+" "); }else{ t1.setText(result+" "); } }else{ t1.setText(""); } }