How can I convert a long to int in Java?

How can I convert a long to int in 开发者_运维问答Java?

---

Updated, in Java 8:

Math.toIntExact(value);

Original Answer:

Simple type casting should do it:

long l = 100000;
int i = (int) l;

Note, however, that large numbers (usually larger than 2147483647 and smaller than -2147483648) will lose some of the bits and would be represented incorrectly.

For instance, 2147483648 would be represented as -2147483648.

---

Long x = 100L;
int y = x.intValue();

---

For small values, casting is enough:

long l = 42;
int i = (int) l;

However, a long can hold more information than an int, so it's not possible to perfectly convert from long to int, in the general case. If the long holds a number less than or equal to Integer.MAX_VALUE you can convert it by casting without losing any information.

For example, the following sample code:

System.out.println( "largest long is " + Long.MAX_VALUE );
System.out.println( "largest int is " + Integer.MAX_VALUE );

long x = (long)Integer.MAX_VALUE;
x++;
System.out.println("long x=" + x);

int y = (int) x;
System.out.println("int y=" + y);

produces the following output on my machine:

largest long is 9223372036854775807
largest int is 2147483647
long x=2147483648
int y=-2147483648

Notice the negative sign on y. Because x held a value one larger than Integer.MAX_VALUE, int y was unable to hold it. In this case, it wrapped around to the negative numbers.

If you wanted to handle this case yourself, you might do something like:

if ( x > (long)Integer.MAX_VALUE ) {
    // x is too big to convert, throw an exception or something useful
}
else {
    y = (int)x;
}

All of this assumes positive numbers. For negative numbers, use MIN_VALUE instead of MAX_VALUE.

---

Since Java 8 you can use: Math.toIntExact(long value)

See JavaDoc: Math.toIntExact

Returns the value of the long argument; throwing an exception if the value overflows an int.

Source code of Math.toIntExact in JDK 8:

public static int toIntExact(long value) {
    if ((int)value != value) {
        throw new ArithmeticException("integer overflow");
    }
    return (int)value;
}

---

If using Guava library, there are methods Ints.checkedCast(long) and Ints.saturatedCast(long) for converting long to int.

---

long x = 3;
int y = (int) x;

but that assumes that the long can be represented as an int, you do know the difference between the two?

---

You can use the Long wrapper instead of long primitive and call

Long.intValue()

Java7 intValue() docs

It rounds/truncate the long value accordingly to fit in an int.

---

Shortest, most safe and easiest solution is:

long myValue=...;
int asInt = Long.valueOf(myValue).intValue();

Do note, the behavior of Long.valueOf is as such:

Using this code:

System.out.println("Long max: " + Long.MAX_VALUE);
System.out.println("Int max: " + Integer.MAX_VALUE);        
long maxIntValue = Integer.MAX_VALUE;
System.out.println("Long maxIntValue to int: " + Long.valueOf(maxIntValue).intValue());
long maxIntValuePlusOne = Integer.MAX_VALUE + 1;
System.out.println("Long maxIntValuePlusOne to int: " + Long.valueOf(maxIntValuePlusOne).intValue());
System.out.println("Long max to int: " + Long.valueOf(Long.MAX_VALUE).intValue());

Results into:

Long max: 9223372036854775807
Int max: 2147483647
Long max to int: -1
Long maxIntValue to int: 2147483647
Long maxIntValuePlusOne to int: -2147483648

---

If direct casting shows error you can do it like this:

Long id = 100;
int int_id = (int) (id % 100000);

---

In Java, a long is a signed 64 bits number, which means you can store numbers between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807 (inclusive).

A int, on the other hand, is signed 32 bits number, which means you can store number between -2,147,483,648 and 2,147,483,647 (inclusive).

So if your long is outside of the values permitted for an int, you will not get a valuable conversion.

Details about sizes of primitive Java types here:

http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

---

In Java 8 I do in following way

long l = 100L;
int i = Math.toIntExact(l);

This method throws ArithmaticException if long value exceed range of int. Thus I am safe from data loss.

---

Manual typecasting can be done here:

long x1 = 1234567891;
int y1 = (int) x1;
System.out.println("in value is " + y1);

---

If you want to make a safe conversion and enjoy the use of Java8 with Lambda expression You can use it like:

val -> Optional.ofNullable(val).map(Long::intValue).orElse(null)

---

long x;
int y;
y = (int) x

You can cast a long to int so long as the number is less than 2147483647 without an error.

---

I'm adding few key details.

Basically what Java does is truncate long after 32 bits, so simple typecasting will do the trick:

    long l=100000000000000000l;
    System.out.println(Long.toString(l,2));
    int t=(int)l;
    System.out.println(Integer.toString(t,2));

Which outputs:

101100011010001010111100001011101100010100000000000000000
                          1011101100010100000000000000000

for l=1000000043634760000l it outputs:

110111100000101101101011110111010000001110011001100101000000
                             -101111110001100110011011000000

If we convert this -101111110001100110011011000000 in proper two's compliment we will get the exact 32-bit signed truncated from the long.

---

// Java Program to convert long to int
  
class Main {
  public static void main(String[] args) {
  
    // create long variable
    long value1 = 523386L;
    long value2 = -4456368L;
  
    // change long to int
    int num1 = Math.toIntExact(value1);
    int num2 = Math.toIntExact(value2);
      
    // print the type
    System.out.println("Converted type: "+ ((Object)num1).getClass().getName());
    System.out.println("Converted type: "+ ((Object)num2).getClass().getName());
  
    // print the int value
    System.out.println(num1);  // 52336
    System.out.println(num2);  // -445636
  }
}

---

long x = 3120L; //take any long value int z = x.intValue(); //you can convert double to int also in the same way

if you needto covert directly then

longvalue.intvalue();

---

I Also Faced This Problem. To Solve This I have first converted my long to String then to int.

int i = Integer.parseInt(String.valueOf(long));

---

Long l = 100;
int i = Math.round(l);

---

In Spring, there is a rigorous way to convert a long to int

not only lnog can convert into int,any type of class extends Number can convert to other Number type in general,here I will show you how to convert a long to int,other type vice versa.

Long l = 1234567L;
int i = org.springframework.util.NumberUtils.convertNumberToTargetClass(l, Integer.class);