java初级chap03.ppt

3: Controlling Program Flow
Using Java operators
Mathematical operators
Relational operators
Logical operators
Primitive type: ALL (the same with C)
String: + +=
All Objects: = == !=
Assignment/Aliasing during method calls
Primitive type: byvalue (copy)
Objects: byRef
Sample-1 sample-2
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class Number {
int i;
}
public class Assignment {
public static void main(String[] args) {
Number n1 = new Number();
Number n2 = new Number();
= 9;
= 47;
("1: : " + +
", : " + );
n1 = n2;
("2: : " + +
", : " + );
= 27;
("3: : " + +
", : " + );
}
} ///:~
9
47
n1
n2
9
47
n1
n2
1: : 9, : 47
2: : 47, : 47
3: : 27, : 27
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class Letter {
char c;
}
public class PassObject {
static void f(Letter y) {
= 'z';
}
public static void main(String[] args) {
Letter x = new Letter();
= 'a';
("1: : " + );
f(x);
("2: : " + );
}
} ///:~
1: : a
2: : z
public class PassPrimitive {
static void f(char y) {
y = 'z';
}
public static void main(String[] args) {
char x ;
x = 'a';
("1: x: " + x);
f(x);
("2: x: " + x);
}
} ///:~
1: x: a
2: x: a
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Relational operators
All type (including boolean): == !=
All primitive type but boolean: All Relational operators
< > <= >= == !=
Logical Operators
AND : &&
OR : ||
NOT : !
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Testing object equivalence
Primitive type: compare value(== !=)
int i=2; if ( i= =2) …
Objects: compare reference(handle) == !=
String s=“AAA”; String ss=s; if(s = = ss)…
String s=“AAA”; if(s = = new String(“AAA”) )…
SPECIAL CASE: String s=“AAA”; if(s = = “AAA”)…
Objects: compare valu