In Java, the difference between new String(), "", and null
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String a = new String();
String b = "";
String c = null;
testString(a);
testString(b);
testString(c);
}
private void testString(String str){
if (str == null){
Log.e(“testNull”, “null”);
}
if (str.isEmpty()){
Log.e(“testNull”, “isEmpty”);
}
if (str.equals("")){
Log.e(“testNull”, “引号”);
}
Log.e(“testNull”, “----------------”);
}
Since I only play Android, I wrote an Android demo. The effect is the same~ The
log result is:
02-15 14:41:10.655 31875-31875/uding.testanimation E/testNull: isEmpty
02-15 14:41:10.655 31875-31875/uding.testanimation E/testNull: quotation mark
02 -15 14:41:10.655 31875-31875/uding.testanimation E/testNull: ----------------
02-15 14:41:10.655 31875-31875/uding.testanimation E /testNull: isEmpty
02-15 14:41:10.655 31875-31875/uding.testanimation E/testNull: quotation marks
02-15 14:41:10.655 31875-31875/uding.testanimation E/testNull: ------- ---------
02-15 14:41:10.655 31875-31875/uding.testanimation E/testNull: null
Then str reported a null pointer error. Here you can find that the effect of isEmpty and "" are the same.
Look at the source code of isEmpty again:
public boolean isEmpty() { return count == 0; } It means that as long as the number of text in the String is 0, it returns true, and the number of text in "" is 0.
To sum up:
null is the "empty" of unallocated memory space ~
isEmpty and quotation marks are the two "empty" relative to null (that is, they!= null), and they are all allocated memory (it seems to have almost the same meaning)
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Original link: https://blog.csdn.net/violetjack0808/article/details/50668195