Java检查字符串是否为null或空

我得到了一些字符串，并在使用图表上的值之前执行了一些检查。这是我的密码：

for (int j = 0; j < shareByTypeList.size(); j++) {
            if (j == 0) {
                facebookShare = shareByTypeList.get(j).getTotalShare();
            } else if (j == 1) {
                googleplusShare = shareByTypeList.get(j).getTotalShare();
            } else {
                twitterShare = shareByTypeList.get(j).getTotalShare();
            }
        }

        if (facebookShare != null && !facebookShare.isEmpty()
                && twitterShare != null && !twitterShare.isEmpty()
                && googleplusShare != null && !googleplusShare.isEmpty()) {
            txtDisplayFacebook.setText(facebookShare);
            txtDisplayTwitter.setText(twitterShare);
            txtDisplayGooglePlus.setText(googleplusShare);
            totalShare = Integer.parseInt(facebookShare)
                    + Integer.parseInt(googleplusShare)
                    + Integer.parseInt(twitterShare);
            txtDisplayShareAmt.setText(String.valueOf(totalShare));
        }

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我通过分离3个变量来执行检查，然后将值设置为textview来解决这个问题：

if (facebookShare != null && !facebookShare.isEmpty()) {
            txtDisplayFacebook.setText(facebookShare);
        } else if (twitterShare != null && !twitterShare.isEmpty()) {
            txtDisplayTwitter.setText(twitterShare);
        } else if (googleplusShare != null && !googleplusShare.isEmpty()) {
            txtDisplayGooglePlus.setText(googleplusShare);
        }

        if (!txtDisplayFacebook.getText().equals("0")
                && !txtDisplayTwitter.getText().equals("0")
                && !txtDisplayGooglePlus.getText().equals("0")) {
            totalShare = Integer.parseInt(facebookShare)
                    + Integer.parseInt(googleplusShare)
                    + Integer.parseInt(twitterShare);
            txtDisplayShareAmt.setText(String.valueOf(totalShare));
        }

---

粘贴堆栈跟踪？它必须是不同的一行。哪一行是第191行？你能告诉我们哪一行是空指针出现的吗？你能准确地指定哪一行是第191行吗？请…你给出了3个变量的默认值吗？

if (facebookShare != null && !facebookShare.isEmpty()) {
            txtDisplayFacebook.setText(facebookShare);
        } else if (twitterShare != null && !twitterShare.isEmpty()) {
            txtDisplayTwitter.setText(twitterShare);
        } else if (googleplusShare != null && !googleplusShare.isEmpty()) {
            txtDisplayGooglePlus.setText(googleplusShare);
        }

        if (!txtDisplayFacebook.getText().equals("0")
                && !txtDisplayTwitter.getText().equals("0")
                && !txtDisplayGooglePlus.getText().equals("0")) {
            totalShare = Integer.parseInt(facebookShare)
                    + Integer.parseInt(googleplusShare)
                    + Integer.parseInt(twitterShare);
            txtDisplayShareAmt.setText(String.valueOf(totalShare));
        }