Dart语言里一切皆为对象,所以如果没有将变初始化,那么它的默认值为null
void testData() {
//Number包含了int和double
int a = 4;
int b = 8;
print(a + b);
int a1;
if (a == null) {
print('a == null');
} else {
print('a != null');
}
if (a1 == null) {
print('a1 == null');
} else {
print('a1 != null');
}
double c = 5.9;
double d = 6.4;
print(c + d);
//String类型
var chen = 'chen';
var yu = 'yu';
var name = chen + yu;
print(name);
var hello = '''
hello word
public static void main1
''';
print(hello);
var word = """
hello word
public stati void main2
""";
print(word);
//Boolean类型
bool isSelect = false;
if (isSelect) {
print('isSelect is true');
} else {
print('isSelect is false');
}
//List类型
var list = [];
list.add(1);
list.add(2);
print(list);
print('size is ${list.length}');
list.removeAt(0);
print(list);
print('size is ${list.length}');
//Map类型
var week = {'one':'test1', 'two':'test2'};
print(week);
print('week length is ${week.length}');
week.putIfAbsent('three', () => 'test3');
print(week);
print('week length is ${week.length}');
}
I/flutter (24359): 12
I/flutter (24359): a != null
I/flutter (24359): a1 == null
I/flutter (24359): 12.3
I/flutter (24359): chenyu
I/flutter (24359): hello word
I/flutter (24359): public static void main1
I/flutter (24359):
I/flutter (24359): hello word
I/flutter (24359): public stati void main2
I/flutter (24359):
I/flutter (24359): isSelect is false
I/flutter (24359): [1, 2]
I/flutter (24359): size is 2
I/flutter (24359): [2]
I/flutter (24359): size is 1
I/flutter (24359): {one: test1, two: test2}
I/flutter (24359): week length is 2
I/flutter (24359): {one: test1, two: test2, three: test3}
I/flutter (24359): week length is 3
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